It was in the summer of 1889 that an invitation reached me, coming from the Royal Physical Society (Koninklijke Natuurkundige Vereeniging) in Batavia, to undertake a trip to the Indian Archipelago for purposes of scientific research. This invitation opened the prospect of realisation of a wish long cherished and for a naturalist not exorbitant,—the wish to have a direct glimpse and a personal impression of animal and vegetable life in the tropics. And so it was accepted with alacrity.
With Plates 9—12.
Now that I am going to give a summary account of my investigations during this temporary sojourn in India, the results of which are gradually taking a shape that will permit of their successive publication, I cannot refrain from expressing my grateful indebtedness to the above-named Society and to its Council. Although the funds that were required-for these researches have been granted by the Government, to whom I am for that reason equally indebted, still it was the Society who transferred the responsibility for the way in which the money was to be spent entirely to me, with what I would be inclined to call a blind confidence.
In consequence of this I was quite free in the choice of any research I might wish to undertake, and also in the method according to which I should desire to conduct both the collecting and the working out of the subject-matter of these investigations. I resolved to extend certain researches with which I had been occupied for the last few years, and which had reference to the earliest developmental stages and the formation of the germinal layers of mammals, as well as to the numerous and often unexpected points of difference which we observe in the first origin and in the detailed anatomy of the placenta (afterbirth) of different mammals.
Of late years the mammalian placenta has been more closely studied by numerous anatomists, but nevertheless its highest stage of differentiation as found in the human subject is yet so imperfectly understood (genetically) that a comparative investigation of the more primitive orders of mammals is an imperious necessity. As in all other attempts at comparative analysis, so in this case the selection of the material that is to furnish the bases of comparison is most important.
Now the lowest mammals (Ornithodelphia, Didelphia) are as yet deprived of a placenta; this organ has only become developed in later, more highly differentiated orders. It is thus the very youngest organ which we meet with in mammals, the latest acquisition by the gradual perfecting of which they have obtained a considerable advantage over the lower Vertebrates.
The order of the Insectivora is regarded as being the most archaic among the Mammalia Placentalia, both on account of palæontological and of anatomical data. And so the objects of comparison had to be chosen in the first place among these more primitive forms.
Several years ago I commenced to study the process of placentation in three European representatives of the order Insectivora—the hedgehog, the mole, and the shrew,—and have published part of the results of these investigations.
In the Indian Archipelago other genera of the same order occur which are entirely absent in Europe. Towards these my attention had in the first place to be directed during my stay in the Archipelago. They are the genera Tupaja and Gymnura, of which the latter very soon proved too rare to be available for this investigation. Tupaja, on the contrary, is much more common, and I might safely feel hopeful to collect a rich harvest of Tupaja javanica.
Besides the additional genera of the order of the Insectivora, the investigation had in the second place to be directed towards another order which is said to occupy an intermediate place somewhere between the Insectivora and the highest order, that of the Primates, to which man and monkeys belong. This intermediate order is that of the Lemuridæ or Prosimiæ. In Europe it is no longer represented by living genera, although in earlier geological periods it did occur in this part of the world. A small number of genera compose this order, by far the majority of them being found in Madagascar.
Two representatives of the Prosimiæ occur in the Indian Archipelago, viz. Nycticebus and Tarsius. A peculiar genus of mammals, the so-called flying maki or Galeopithecus—different in organisation as well as in mode of life—was at one time regarded by zoologists as being more closely allied to the Lemurs, at another time to the Insectivora or to the Cheiroptera, or even as an order by itself (Dermoptera). This genus also occurring in the Indian Archipelago, it had similarly to be included in the sphere of the projected investigation.
Finally, I was interested in the only representative of the order of the Edentata that has as yet been brought to light in the Indian Archipelago, viz. Manis javanica, and desirous to obtain a complete series of the different stages of placentation of this animal; the Edentates presenting considerable differences among themselves with respect to their placentation.
Coloured drawings of the above-named mammals were distributed, a few months before my arrival in India, by the Royal Physical Society amongst a number of persons with whom readiness to co-operate appeared probable.
To this was added a circular, answers to which successively arrived. My friend Dr. P. C. Sluiter, librarian to the Society, to whose energetic assistance I am deeply indebted, entered into a preliminary correspondence with the writers, and placed the outcome of this at my disposal when I arrived in Batavia in November, 1890.
In this way matters were made easy for me, and I could form a provisional opinion as to the question in which part of the Archipelago I would probably find the most favorable collecting spots.
Only certain general data were available as to the habitat of the above-named genera of mammals, but detailed accounts about their comparative rarity, by which certain regions might at the outset be considered as less favorable than others, were deficient, as were also reliable data about their time of reproduction, &c.
Moreover, different aspects of the question must be kept sight of. Suppose the animals to be numerous in a region without European inhabitants, I could not then expect a rich harvest. Similarly it might be presumed that in parts where the population is scarce, the inhabitants could hardly give any important aid in the collecting of a great number of specimens.
On the contrary, it was most probable that in strongly populated districts where a large proportion of the soil is cultivated, the mammals in question would be very rare or extinct. It was, in short, unavoidable to spend the months of my stay in India in as considerable a number of different places as possible. In this way I was able to enter into personal connection with very many who might be willing to continue the collecting business even after my departure. For this purpose I left behind me, wherever I had succeeded in enlisting cooperators, printed instructions, chemicals, glass tubes, &c., as well as cash for the payment of premiums to the natives by whom the collecting of the live material was to be done.
This method of going to work must appear to be a tedious and slow one. At the same time it was in the commencement most undoubtedly disheartening. Still I have conscientiously applied it wherever I have stayed, after generally demonstrating by means of more common animals than those I was in search of how the extirpation of the uterus had to be effected, and how the preservation was to be done. Now that three years have passed by, I may safely say that the results have far surpassed my expectations.
Among the hundreds of persons with whom these roamings through the woods and mountains of Java, Sumatra, Banka, Billiton and Borneo have brought me into close connection, and who have been interested in the object of my investigations as explained to them by me, it is only natural that the great majority has been unable by various circumstances to contribute in any way towards the increase of my embryological collection.
They, however, who have thus contributed can hardly have imagined how their apparently small collections—but which are being forwarded from numerous parts—can together constitute a very considerable array of important material for research. Such has undoubtedly been realised on this occasion, considering that at this present moment I already dispose of—
making the respectable total of 1026. This collection is yet increasing continually by new arrivals.1
The majority of these uteri are pregnant in one stage or the other ; many have been preserved very shortly after parturition ; only a very few are virginal.
The pregnant uteri contain the most divergent stages, from the earliest phases of segmentation to the nearly ripe or newly born fœtus. Several newly born young have also come into my possession, as also a few in the very act of birth, the nearly born fœtus being still connected by its umbilical cord with the as yet adherent placenta.
The numerous microscopical preparations which have already been made of the rich and varied material demonstrate the perfect care which most of my correspondents have bestowed on the preservation. Consequently the histological details of the placentation process, of the formation of the germinal layers, and of the ontogenesis can be studied from these preparations quite as satisfactorily as if the preparations had been freshly made in the laboratory.
Again in this respect Kleinenberg’s mixture (picro-sulphuric acid) has proved to answer to a very high standard of excellence; in the case of the preservation of uteri in toto it gives the best chances for the finer details of early blastocysts therein enclosed, or of the placentary structures in the course of formation, to be perfectly preserved ; always on this sole condition, on which I have everywhere laid particular stress, that the extirpation be made instantly after death. Preparations made from animals that had been dead even for only a very short time have already undergone so considerable an alteration that they are of very inferior value for comparative and especially for histological research.
A point which had more particularly puzzled me before I commenced my peregrinations was the question at which period of the year the animals I was going to search for reproduced their species. As was already noticed above, the literature on the subject leaves us entirely in the dark with respect to this point. And though the alternation of seasons is much less marked in the tropics than in the temperate regions, still the regular succession of the “rainy” monsoon and of the “dry” monsoon—more marked, however, in certain parts of the Archipelago than in others—might be expected to have a certain influence on the birth-rate and on the association of the sexes in these animals.
If in the commencement I have been inclined to believe that it would be possible to detect any such parallelism, still, as the collections have increased, it has become more and more evident that reproduction of the species investigated occurs all the year round.
In the same months the most divergent stages of pregnancy have been observed to occur ; in no month have they been deficient. My different correspondents have come to the same conclusion as soon as the material they brought together became more extensive, and allowed them to compare the results of different months.1
Another general conclusion, which has more especially been verified for Tupaja and Tarsius, is that pregnancy is repeated at rapid intervals, very early stages of development being often found in the same uterus simultaneously with the yet indubitable remains of a preceding pregnancy, as judged from the unmistakable traces of a preceding placentation, from the nature of the uterine wall and the uterine vessels, &c.
In the case of Galeopithecus it twice occurred that a young animal was yet being suckled by the mother and was found attached to. her breast, whereas autopsy shnwed an already fairly advanced younger foetus to be present in the uterus of the same specimen.
The fact that all the species here mentioned bring forth only one young at a time (Tupaja, which regularly carries two foetus simultaneously, alone excepted) may perhaps account for the prolific properties here referred to, being developed as a counterbalancing agency to this restriction of the number contained in one litter. In our European Insectivora, whose time of reproduction is limited to only a few months or even weeks in the year, the litter normally amounts to eight (Sorex) or six (Erinaceus, Talpa) young ones.
Of all the cases that have as yet come under my observation I know of only one case of twins in Nycticebus. They were enclosed each in a different horn of the uterus, whereas in the normal cases one of the two horns is always barren.
In Tarsius, Galeopithecus, and Manis I have never noticed more than one young at a time. In Tupaja never more and never leas than two are present, occupying the right and the left half of the uterus.
There, as formerly in Sorex, I have, however, been able to establish without doubt that the number of fecundated eggs and even yet of early blastocysts is constantly found to be more considerable than the number of ripe foetus that attain maturity and form the normal contents of a litter.
Thus in Tupaja four and sometimes more blastocysts are found in early stages, apparently all of them in equal conditions of vitality. A struggle between these blastocysts for the definite attachment to the maternal uterine wall is thus inevitable. How this struggle is brought about and what points finally decide between those that shall thrive and those that shall perish is at present obscure. Still the fact has no doubt a definite significance, considering that it is not a casual observation, but a most regular occurrence in at least two genera of Insectivora.
My preparations are not yet numerous enough to allow me to speak with the same emphasis for the other genera.
Attention will of course have to be directed to this point, in order to make out whether it may be regarded as a general rule in mammals that more blastocysts than can partake in the normal course of intra-uterine development are present in the earliest days after fecundation has taken place.
One question to which my preparations do not allow me to reply is that concerning the duration of pregnancy in the five species investigated. The lapse of time that occurs between the date of fecundation and that of parturition is in no way indicated even by the most complete set of intermediate stages between the cleaving egg and the ripe fœtus. On the other hand, it is in no way of any importance for the correct interpretation of the different and successive ontogenetical processes to be acquainted with the exact rate at which these stages succeed one another, or with the age of any particular stage as expressed in a fixed number of days.
With animals bred in domesticity this is of course easily accomplished. But then, on the other hand, the domestic animals have in later years been often shown to furnish us with data that are more liable to a certain amount of divergence than those which have been obtained from animals living in absolute freedom. There can hardly be a doubt that the inevitable pammixia which accompanies domestication can alter and render variable parts of the organism both internal and external, which have a more fixed standard in their nondomesticated congeners.1
For this reason the study of mammalian ontogeny, not from the rabbit and the Cavia, but from specimens of other species and genera captured in their natural haunts, deserves special recommendation.
The object of this paper being to establish certain general facts that come to light when the pregnant stages of the five genera in question are compared macroscopically, and before the microscope is as yet brought to bear on the numerous and intricate questions of histological detail, it will recommend itself to treat the five genera separately.
TARSIUS SPECTRUM. FIGS. 1, 2, 18—21,47—49
There can be no question that all the specimens obtained by me belong to Tarsius spectrum, Pall., and not to Tarsius fuscomanus, Fisch. The differences between these two species have lately been fully discussed by Weber in vol. iii, p. 260, of his ‘Zoologische Ergebnisse einer Keise in Niederlandisch Ost-Indien,’Leiden, 1893. None of the uteri in my collection were obtained from the localities to which Tarsius fuscomanus is restricted. The name by which Tarsius is known to the natives in South-west Sumatra is singo puar ; those of Banka call it the berook puar, or mentiling; those of West Borneo, tempiling.
In a yet higher degree than the other Prosimiæ, Tarsius was recognised by the older anatomists to be intermediate between Insectivora and Primates. Burmeister, in the preface to his ‘Beitrage zur naheren Kenntniss der Gattung Tarsius,’ writes as follows (p. 6) :—” Tarsius possesses, in addition to its considerable external similarity to monkeys, the most complete insectivorous dentition which Quadrumana can boast of, for even the incisors have adopted the type of the canines, and have thus become eminently like the true dentition of the Insectivora. In this Tarsius differs from all other Prosimiæ.”
The non-pregnant uterus of Tarsius has been figured on pl. 6, fig. 22, of the above-mentioned work.
The author thus describes the internal female organs :— “They consist of two small ovaries, the coiled oviducts, and the two-horned uterus…. The ovaries are small spherical bodies, half a line in diameter; their surface is quite smooth, and their inner substance is of the ordinary condition of that of the higher mammals…. The uterus is two-horned, each horn being three inches long ; then follows the unpaired portion, which attains to half an inch, and externally passes into the vagina without any interruption. On the inner surface I could, however, detect a faint boundary as an ostium uteri. The uterus horns, as well as the unpaired portion, have thick walls, and show numerous considerable folds.”
I have now before me several dozens of non-pregnant and early pregnant Tarsius uteri, and I have little to add to Burmeister’s observations. There is, however, very often a strongly marked difference in size between the two ovaries, one swelling up to the size of a pill, the other remaining considerably smaller. I was inclined to believe that this difference in size might go parallel with fecundation, and thus indicate the presence of an early developmental stage in a uterus with one of the ovaries thus swollen. Series of sections in which the uterus lumen and that of the oviduct have been most carefully scrutinised, oblige me to give a negative answer to this conjecture. The cause of this swelling of one of the ovaries was investigated, and will be treated of elsewhere, It was more than once noted in the fresh animal before preservation by one of my correspondents, to whom I am indebted for most valuable material.
Concerning the aspect of the internal genital organs of Targius when fresh and in situ, he tells me that the colour of the ovaries is often very different. Sometimes pink, they are at other times of a lighter and darker yellowish hue ; and in young specimens they have the appearance of a small row of spherical or rod-like bodies of a light yellow colour. I have not yet found time to study the sections of the young stages of the ovaries thus characterised.
The body of the uterus with its double horns of the preserved specimens in my possession is extremely variable in shape according to circumstances. It is difficult to detect the very early stages of pregnancy at first sight.
Yet long before the embryo has proceeded so far that the medullary groove has made its first appearance on the surface of the blastoderm, there is a very marked swelling of the uterine half in which the blastocyst has come to adhere.
This uterine swelling is in no way perfectly spherical, but more saddle-shaped, in accordance with the fact that even in these early stages the blastocyst adheres to the maternal tissue in one particular region, and not along any more extensive surface, as, for example, in the shrew, the mole, the hedgehog, &c.
The details of this process will be fully described elsewhere. I may here add that this early point of attachment corresponds in situation to what will, in a later stage, become the placenta, and that no omphaloidean attachment, precedes as a temporary structure the definite placentary connection.
When pregnancy advances it can be noted that the placenta does not occupy a varying but, on the contrary, a fixed position with respect to the different regions of the uterus. It is always situated close to the apex of the horn on the mesometrical side, and the swelling of the uterine walls is not most conspicuous close to this point of attachment, but more towards the vaginal portion of the horn (cf. fig. 1). It is in this more extended part of the uterus that the head of the full-grown fœtus is situated, which is thus normally the first to pass outwards at birth (cf. fig. 18).
When a uterus containing a ripe or nearly ripe fœtus is carefully opened by a longitudinal incision, there is seen to be no adhesion whatever except in the placentary region (figs. 18— 21). The uterine walls are stretched to an extreme degree of tenuity ; indeed, so thin have they become that even in the specimens that were preserved in spirits, and have thereby considerably increased in opacity, the limbs, the ears, the fingers, and the tail of the fœtus can be distinguished through this thin layer of maternal tissue.
Immediately beneath the stretched uterine wall the fœtal envelopes form a very tight sac containing the fœtus. This sac is so transparent that in spirit specimens the individual hairs on the head, body, and limbs, the nails, &c., can be recognised through it (figs. 18 and 47).
Towards the tail end of the fœtus the fœtal envelopes pass into a button-like projection, which constitutes the placenta. Figs. 18, 19, and 47 show this both in the front view and in profile ; in fig. 20 the longitudinal section indicates still more clearly the way in which the thin fœtal envelopes merge into the placentary tissue. It is, moreover, visible, both in fig. 18 and in the longitudinal section (fig. 20), that the placentary knob itself adheres with the maternal tissue only along a very limited extent of its total surface, viz. a squarish area in which numerous lumina are visible (figs. 18 and 47), when the placenta is loosened from the maternal tissue by a slight shaking. These lumina are formed by the tracts which convey maternal blood to and from the placenta. Microscopical examination of thin sections through this region reveal without any doubt that, indeed, this limited area is the only point of fusion, the remaining surface of the placenta being as little fused with the maternal tissues opposite to it as are the fœtal membranes themselves. About the histology and the genesis of the placenta of Tarsius I will treat in a later paper; suffice it to say that, according to the nomenclature now in use, the Tarsius placenta would be directly classed with the discoid type. It has not the faintest trace of any relation whatever to the diffuse type, which was hitherto considered as being the type of placenta to which the Lemuridæ belong.1
The umbilical cord by which the embryo is connected with the placenta is comparatively short ; it is represented in figs. 20 and 21, containing very prominent vessels.
In fig. 21 the ramification of these vessels on the placenta is, moreover, indicated as this is seen (in a spirit specimen) after the removal of the foetus. Fig. 49 represents the fœtal membranes and the placenta with severed umbilical cord after they have been removed out of the uterus, and the fœtus has passed out of its envelopes.
These envelopes having here been preserved after the fœtus had been expelled are less stretched and transparent than those of figs. 18 and 47. The afterbirth of Tarsius (which is expelled in the customary way and not resorbed in situ, as that of Talpa) consists of these same parts; the envelopes are then more folded together against the knob-like placenta than in fig. 49.
Embryos of Tarsius are in my possession from the earliest stages of segmentation up to the newly born young. Two of them are represented in figs. 46 and 48. In the first the comparatively large size of the head is worthy of note ; in the second the way in which limbs, fingers, and tail are tightly folded together against the body in a small compass deserves special attention.
The details of the ontogeny of Tarsius, which as yet has never been investigated embryologically, I hope to be able to work out soon with the aid of the very complete material now at my disposal.
With respect to the details of the placentation process I will also have to refer to a later publication, and can only state that the trophoblast of the very early two-layered blastocysts undergoes a most considerable amount of proliferation at the spot where the uterine surface has in its turn undergone certain differentiations intended for the future attachment of the blastocyst. This proliferation, the products of which undergo remarkable further developmental changes, eats its way very deeply into the maternal tissue between the tubular uterine glands.
Vascularisation of this proliferated region, which fuses in a particular way with the surrounding maternal elements, is then brought about, for maternal blood circulates in it freely and copiously, and soon another system of vascular channels connects the growing embryo with this rich source of energy.
A very early and profuse growth of mesoblastic tissue plays an important part in this secondary connection between the growing foetus and its chorion, and accentuates in a suggestive way the several features by which Tarsius approaches the Primates.
However, I shall have to postpone a detailed description of this point to a later publication.
Nycticebus. Figs. 3—5, 22, 23, 30—40, 50—56
This second genus of Prosimiæ, represented in the Archipelago by the species Nycticebus tardigradus and N. javanicus,1 is known by a series of names which have much the same sound, but in which the consonants vary according to the different regions. These names are—kukang, tukang, pukang, and huhang. In East Sumatra and Banka the name of berook semoendi is in vogue among the natives. In East Java specimens were especially difficult to procure because the skeleton is said to be most efficacious in bringing about death and destruction among the unfortunate inhabitants of a house in front of which it has been buried overnight. It is thus in high demand among the wealthier natives who have family quarrels to settle, and I have known exorbitant prices, with which a collecting embryologist could not possibly compete, to be stealthily paid for one specimen, for this unfriendly though perhaps harmless purpose.
As will be seen, Nycticebus differs most considerably from Tarsius in several important respects.
The stages of pregnancy, as studied from the unopened uterus, are not characterised by any very marked peculiarity. In the three uteri figured on Pl. 9 the ovary is seen to be more or less concealed by a mesenterial fold, which contains the Fallopian tube, whereas the two horns of the uterus have a peculiar asymmetrical shape, being rounded dorsally and pointed ventrally. This latter detail, which can be easily recognised in the uteri that are young or in early stages of pregnancy, is of course lost as the swelling of the pregnant horn increases. Still, even then it can yet for a very long time be detected in the non-pregnant horn.
In the literature on the Mammalia I do not find any other representation of the uterus of Nycticebus than those contained in Kuhl’s “Einiges fiber die Splanchnologie von Stenops gracilis “(Beiträge zur ‘Vergl. Anatomie, zweite Abtheilung,’ p. 37, pl. 6, Frankfurt, 1820) ; and in Schroeder van der Kolk’s papers, ‘Bijdrage tot de Anatomie van den Stenops kukang’ (‘Tijdschrift voorNat. Gesch. en Physiol.,’ vol. viii, pl. 5, figs. 8 and 9, Leiden, 1841). This latter figure is most insufficient, and does not in any way indicate the peculiarity just mentioned. Moreover in these figures other peculiarities—for example, an abnormal extremity of the Fallopian tube (1. c., fig. 9)—are represented, and a total absence of fimbria is noticed which does not conform to the actual facts, and which differs markedly from what figs. 3 and 7 teach ns. V. d. Kolk’s specimens must have been somewhat mutilated and perhaps imperfectly preserved.
The first pregnant uterus of Nycticebus which I opened was the object of particular expectancy. Knowing that for the Madagascar Lemuroids (Propithecus, Indris, Avahis) both Milne Edwards1 and Turner2 had described and figured a diffuse placenta, which was, however, first distinctly recognised as such by the latter, and that Tarsius in this respect reveals such a totally different arrangement, it was of course of a double interest to know whether Nycticebus would conform with either of these types, or would represent one by itself.
The first dissection which I ventured to make was for this reason effected with special precautions. It is represented in figs. 22, 30, and 36, and from the first of these three figures it will be seen that, to begin with, the muscularis was carefully peeled away. The outer surface of the mucosa thus brought to light revealed (by transparency) the presence of a network, the meshes of which are visible to the naked eye. The character of this network could be better recognised as soon as the incisions had been made that are represented in fig. 30, M being the same flaps of the muscularis that are indicated in fig. 22.
The mucosa (nt) was seen to present projecting ridges arranged in reticular fashion, and between which polygonal areas were thus enclosed, into which villiform protuberances of the underlying foetal envelopes were seen to fit. So loosely did they fit, however, that no traction whatever was required to sever the connection between chorion and mucosa all along this spherical surface. The fœtus with its envelopes could be floated out of the mucosa the moment the preparation represented in fig. 30 were to be turned upside down.
The reticular surface of the mucosa is seen in a much more natural connection of the parts in figs. 23, 31, and 32, where the uterus has been opened and the flaps cut out of the wall have been folded back. The mucosal network and the muscularis have here remained unseparated. Still it was quite as easy to remove them from the subjacent fœtal envelopes as it was in the foregoing case.
And so all these preparations leave no doubt that with respect to the connection between mother and fœtus Nycticebus resembles ever so much more closely the Madagascar Prosimiæ than it does Tarsius.
However, there are differences between the Madagascar genera and Nycticebus that deserve special mention. Firstly, the maternal network in the former (Milne Edwards, 1. c., pl. 114, fig. 1) is much less decidedly reticular, and, on the contrary, more lamellar than what is here represented (figs. 38, 51, 52, 56) for Nycticebus. Turner’s figs. 6 and 8 (also taken from Madagascar lemurs) agree very closely with those of Milne Edwards. Secondly, the outer surface of the fœtal envelopes is very much the counterpart of the maternal arrangement, as can more especially be seen from Turner’s figs. 3, 4, and 12; but also from Milne Edwards’ pl. 114, 117 (3), and 118 (1). And in this respect Nycticebus presents the same phenomenon of concordance between the fœtal excrescences and the maternal crypts, so that, instead of the lamelliform arrangement of the chorionic surface so conspicuous in the Madagascar lemurs, we here find circumscribed short columnar villi, each one of them fitting into a corresponding depression of the maternal reticulum. These columnar villi are quite equally distributed over the whole surface of the chorion, as is more particularly indicated in figs. 23, 31, 50, and 53. As pregnancy draws to its close, these chorionic villi disappear on a restricted chorionic area, which covers the head of the fœtus and is directed towards that side where the corpus uteri and vagina are situated. The maternal surface opposite this part of the chorion is similarly non-reticulated. A flattened projection of the chorion, similarly without villi, is sometimes found attached to this anterior surface of the chorion. Both on the latter and on the projection here alluded to we find that the epithelial recesses, which will be mentioned lower down, are, all the same, present. The greater part of the chorion just before birth is, however, densely covered with the particular villi that indent into the maternal reticular crypts. The transitional region between the areas is represented in fig. 55.
In fig. 35 the fœtal envelope is seen in natural size, and between the villi numerous openings (ap.) are detected. In the earlier stages these openings are also already present, and can be easily seen with a lens or even with the naked eye. If we open the chorion enveloping the fœtus (fig. 30) we find the inner surface of what was the villiferous covering of the fœtus to be flat, and this inner surface to be only here and there interrupted by round patches (R), each of which corresponds to one of the openings (ap) just mentioned. Of these relations of the parts, figs. 30, 32, 34, and 36 give further elucidation, whereas the definite proof of the correspondence of the flattened and faintly prominent recesses (JR.) with the apertures (ap) can of course be more especially obtained in sections, as that of fig. 39.
The distribution of vessels on the inner surface of the chorionic envelope is more particularly visible in fig. 34; the attachment of the umbilical cord to the same in figs. 32, 33, and 36.
The villi themselves are at first (fig. 50) more cylindrical ; when they increase in age they become folded and wrinkled to a not inconsiderable extent, as is visible in figs. 37 and 37 a. It may be expected that these folds and wrinkles correspond to coordinated arrangements of the reticular layer of the mucosa, the two thus fitting together in a very simple way.
The maternal folds on the mucosa are in the Madagascar lemurs interrupted at regular distances by small bald patches, both according to Turner (1. c., figs. 6, 8, and 9) and to Milne Edwards (woodcut on p. 280).
In these spots the tubular uterine glands open out between the folds that have arisen on the inner surface of the uterus in the course of pregnancy. In Nycticebus I find a more equal distribution, the gland openings being found in the centre of nearly every separate compartment of the reticular arrangement. In fig. 38 this is indicated, the darker shading at the bottom of these compartments representing gland tracts.
Viewed with a pocket lens the openings are often visible as a whitish spot near the middle, where they appear to be more concentrated.
Figs. 39 and 40, drawn with the camera with very low power, give the exact relation of the maternal and the embryonic parts in a section through chorion and uterine wall. Of the latter, muscularis and mucosa are indicated in fig. 40, the elevated ridges of the mucosa that form the peculiar reticulum referred to being visible as so many inward projections. They are all covered by an epithelium which even in this far advanced stage can be readily distinguished. Immediately below this epithelium numerous finely branched maternal blood-vessels take their course, in every respect comparable to those which both Turner and Milne Edwards have made out by injections for the Madagascar Lemuroids.
The chorionic villi of Nycticebus are seen to fit very exactly into these cryptiform spaces ; it is worthy of remark that the epithelium on the villi is in many places ever so much thicker and more considerable than what is found on the opposite maternal surface.
In the villi numerous embryonic capillaries take their course immediately below the epithelial layer. The two vascular surfaces are thus separated only by the thickness of two cell-layers, of which the maternal one is less high and less columnar.
The above-mentioned recesses (R) in the chorion are clothed by a direct continuation of the chorionic epithelium. Smaller vascular villi with a much less massive core of connective tissue stand out into the lumen of these recesses, as can be seen both in fig. 39 and fig. 40.
The amnion which enshrouds the foetus has been partly removed in fig. 30, and is partly folded back (after removal of the foetus) in fig. 32. Also in figs. 36 and 54 it has been dissected away, whereas in these two latter figures the connection between the foetus and the villiferous chorion by means of the umbilical cord is still retained, the chorion being partly inverted in the act of stripping off the embryo.
In the preparations here figured no indication is given of the yolk-sac and the allantois. In Milne Edwards’ figures of Madagascar lemurs a very conspicuous place is allotted to the allantois, which he has inflated, and which thus showed digitate processes and a multilobulate shape. It is thus described as being non-vascular. The exact terms of Milne Edwards are the following (1. c., p. 283) :—” Les parois de l’allantoïde sont délicates et transparentes, aucun vaisseau ne s’y distribue. Si l’on injecte un liquide coloré dans le pédoncule de cette enveloppe membraneuse on peut le suivre dans l’ouraque, à travers le cordon ombilical, jusque dans la vessie urinaire; preuve manifeste que cette poche, malgré ses caractères anormaux, représente exactement Pallantoïde des autres mammifères.”
The above description would suggest other half of the same uterus. The head of that in the Madagascar lemurs the allantois plays a part which is to a certain extent comparable to what Selenka1 has described for Didelphia (1. c., pl. 16, figs. 1—5, pls. 17, 18). But then in Didelphia it is the yolk circulation by which the chorion is vascularised, whereas in Milne Edwards’ lemur foetus he finds the umbilical vesicle to be extremely reduced. Traces of it can only be made out in embryos of very early developmental stages.
This latter fact shows that a comparison with the Didelphia does not carry us very far. The vascularisation of the chorion of the Madagascar lemurs must be a phenomenon sui generis if Milne Edwards’ observations are confirmed; and it will be understood that for this reason an exact insight into the state of affairs as they present themselves in Nycticebus is all the more desirable, especially if all the genetic stages be closely followed, as the now available material promises to admit of.
This will at the same time explain why I wish to refrain from further discussing the point on this occasion.
Still I may be allowed to refer to an earlier publication in which I have insisted on the advisability of restricting the use in mammalian embryology of the name chorion.2 I have there argued at some length why I proposed “henceforth to restrict the use of the term chorion to man, and—dependent upon future researches—perhaps to the Primates.” What Selenka has since made known with respect to monkeys, indeed, shows a close resemblance between man and certain monkeys with respect to these placental phenomena.1 And I would now venture to insert in the above citation, after the word “Primates”: “and to the Prosimiæ.”
In accordance with this it will be seen that in the present paper I have used the term chorion a few times only in reference to Nycticebus and Tarsius, whereas with respect to the other mammals I prefer to employ the term “diplotrophoblast “(1. c., p. 385). It is thereby testified that a foetal envelope is present which is only secondarily vascularised, either by the vessels of the allantois or by those of the yolk-sac.
And thus, for the present, the new data here adduced for Nycticebus are restricted to the fact that the embryo of Nycticebus is enclosed in a complete sac which is entirely covered with thick villi, and which is very loosely attached to the vascular meshes of the mucosa into which the villi fit.
I hope to be able to furnish ample information concerning the ontogenesis of the chorion, &c., in a later publication.
A short reference to the two figures 55 and 56 should yet be made. Fig. 55 is an enlarged photograph of part of the same preparation represented in fig. 35. The actual shape of the villi, their flattening and partial disappearance towards the right extremity, is here better visible than in the lithographic figure.
Fig. 56 shows very graphically what becomes of the earlier network of the mucosa that was represented in fig. 51. The frilling of the border of the ridges, which is not yet present in the latter preparation but which becomes conspicuous in the later phases of pregnancy, is better brought out in this photograph than in the still more enlarged fig. 38.
The big folds that are visible in fig. 56 have arisen in consequence of an intentional folding backwards of the uterine walls.
All around the central depression the reticulation is less marked. Where the mucosa faces the flattened surface at one of the poles of the chorion above alluded to, the reticulation is also deficient.
Galeopithecus. Figs. 6—11, 24—29, 57, 58
Concerning the ontogeny and the placentation of Galeo-pithecus, I could find no data in the mammalian literature but a few lines in an article of Gervais1 on the cerebral conformation of the Mammalia (1. c., p. 425). He does no more than mention the fact that he examined a foetus of Galeopithecus which was shown to possess a discoid placenta. Without entering into any further details, he figures (I. c., pl. 22) the said foetus with outspread patagium and severed umbilical cord (fig. 1), and the same folded together in its intra-uterine position and attached by a thick and short umbilical cord to a disk-shaped placenta on which a number of radiating blood-vessels are indicated.
Gervais’s figure corresponds in a general way with fig. 29 of this paper, only it is much smaller, and was probably not figured natural size. In our fig. 29 the circular placentary area is seen to lie as nearly as possible in the level of the uterine surface, and not to form such a marked button-shaped prominence as, for example, the placenta of Tarsius figured close to it (fig. 20) does to such a considerable extent.
Though both discoid, these two placentas are, no doubt,, also in other respects profoundly divergent from each other. Although I have as yet only a provisional acquaintance with the chief stages of the placentation of Galeopithecus, I can more especially call the attention to the peculiar aspect of the placenta in figs. 24, 25, and 27.
It is already a discoid formation, but in these younger stages it is less compact and less intimately soldered with the uterine walls; the placental vessels, on the contrary, being mutually interwoven in an intricate manner, and being applied as a delicate but prominent web (figs. 24 and 25) against the inner uterine surface.
The foetus is connected with it by means of a short umbilical cord. Besides, there is a vascular connection between the fœtus and the remains of the yolk-sac.
The latter is represented in figs. 26—28, whereas in fig. 24 it has been dissected away in order to show the embryo enclosed by the amnion in its attachment to the placentary region.
In fig. 26 nothing has been removed but the uterine wall. The blood-vessels radiating over the yolk-sac are as distinctly visible as a spirit specimen will admit of. To the right as well as to the left the cut lumina of blood-vessels (cf. figs. 10 and 11) are seen to take their course in the thickness of the uterine wall.
On the right the placenta is represented by one free border, which is, moreover, loosened from any uterine attachment; the rest of the placenta is hidden from view by the embryo and its envelopes.
In the next figure (fig; 27), which has reference to this same specimen, the embryonic sheaths have been opened and the embryo is removed. The membranes to the right are the yolksac and the amnion. At the bottom of the uterine cavity the placenta can be distinguished.
In fig. 28 the embryo with its envelopes and with the placenta has been wholly scaled out of the uterus. Of the placenta an indented border is seen to the left of the figure, whereas to the right only the yolk-sac has been dissected and turned over ; the amnion, however, is still in its place, and hides the embryo from view.
We have now to say a few words concerning the outer aspect of the uterus before and during pregnancy. More than in any of the species hitherto noticed the uterus of Galeopithecus may be said to be double, the vagina being spacious and thick-walled, and the two halves of the uterus (cf. figs. 2, 6 a, 7 a, 8 a, and 9 a) opening out into the vagina by separate openings. There is no unpaired median cavity in common between the two uteri, communicating by means of a single “os uteri “with. the vagina. Still when this proximal portion of the vagina is more closely examined, we find projecting into it a median prominence carrying a uterine crescentiform ostium on its left and on its right surface.
This fleshy projection must be looked upon as the partial soldering in the median plane of the distal parts of the two uteri, the fusion not having gone so far that it affects the uterine cavities.
Pregnancy soon reveals itself by swelling of one of the uteri (figs. 7—11). I have never noticed more than one foetus at a time in Galeopithecus. The earlier swellings do not offer any peculiarity that could not be gathered from the figures 6—9 ; the later swellings, which come to take a marked ovoid shape, are externally characterised by an uncommon distension of vascular tracts in the uterine wall, which even in the preserved specimens stand out—in relief—against the flat outer uterine surface. This is no individual peculiarity, but is noticed in all the uteri of later stages. In fig. 11 the phenomenon is more marked than in figs. 10 a and 10 6; in all of them the central parts of this radiating vascular arrangement correspond with the mesometrium. The situation of the placenta is not in any special relation to this vascular arrangement. The way in which the ovary of Galeopithecus is partly hidden in a mesenterial fold (figs. 7 b and 8b)has a certain resemblance to what was noticed above for Nycticebus and represented in fig. 4.
The fœtus of Galeopithecus that are figured on Pl. 12 (figs. 57, 58) show that the patagium is already indicated at an early moment. Fig. 58 represents, however, a not yet ripe fœtus ; this is figured (natural size) in fig. 29.
After the young Galeopithecus is born it seems to remain attached to the mother’s nipples for a not inconsiderable time, considering that on more than one occasion a pregnant uterus of the size of figs. 9—11 was prepared by one of my correspondents out of a female in which a young animal of the preceding litter was found clinging to the mother’s breast.
Vernacular names for Galeopithecus in the Archipelago are kubin or kubing, krendôh-kentjeng, and walang kêkkes (sometimes also applied to the flying squirrel or walang kôpo).
Tupaja. Figs. 12—17, 41, 59, 60
This small Insectivore, which, as the vernacular name of Tupaj indicates, might easily be confounded with squirrels, was common in the plantations of coffee and cinchona in the Preanger districts. It often goes by the name of coffee rat, kekkès being the name by which the inhabitants of the above-mentioned districts generally designate it.
Tupaja has never more than two young at a time, as was noticed above. A uterus in an advanced stage of pregnancy is represented in fig. 17, the vaginal portion being here cut away. Most marked in this figure is the prominence of two reniform regions in the uterine wall. If the uterus were turned over, two exactly similar patches would be noticed. As in each of the two swellings only one embryo is contained, it follows that the placenta of Tupaja javanica must necessarily be double.1 This is, in fact, the case, the two placentas lying right and left of the foetus. They are connected with it (as fig. 41 distinctly proves) by an umbilical cord. This commences as a single strand of tissue, then bends upwards along the foetus’ side, and only divides into a quadruple set of blood-vessels above the fœtus’ back. Two of these latter strands (each containing two vessels) continue in the same course, and vascularize the placenta which is situated on the side opposite to that where the umbilical cord passes upward, whereas the two other strands bend at an angle of 180° and vascularize the placenta that is on the same side as the umbilical cord. Fig. 41 will make all this clear ; it was taken after one of the two swellings of the uterus was longitudinally cut open, the fœtus being also halved.
The perfect regularity in the situation of the two placentas of each fœtus is a phenomenon in which the maternal tissue plays a prominent part. If we examine transverse sections of very much earlier stages of pregnancy, such as are represented in figs. 12—16, the lateral attachment of these early and much younger blastocysts is seen to have come about in the same spots where afterwards the reniform placenta will develop. The attachment of the early blastocyst, long before any allantois or allantoidean circulation has made its appearance, comes about by means of a very considerable proliferation of the trophoblast. The proliferating patches of trophoblast are double, and face the two spots in the uterine wall alluded to. It is beyond all doubt that even before this proliferation of the embryonic trophoblast has commenced the maternal tissue has become visibly modified in those four regions of the mucosa which correspond to the future placentary region, i. e. the right and left inner surface of the uterus-horn when cut transversely.
The tubular uterine glands are then more particularly limited to the mesometrical and antimesometrical regions of the lumen ; on the spots in question the interglandular connective tissue has proliferated with partial displacement and partial obliteration of the glands there situated.
The uterine epithelium does not take part in this growth. It is, on the contrary, destroyed by the trophoblastic proliferation as soon as the blastocyst commences to adhere. This trophoblastic neoformation is then gradually vascularized (maternal blood penetrating into it), and undergoes a series of interesting but complicated histological transformations. In a future paper I propose to treat this placentation process of Tupaja more fully -, it may here suffice to remark that against these early placentary cushions the yolk circulation is first applied, and that in further stages of pregnancy the yolk-sac is again removed from thence and replaced by the allantoidean blood-vessels which then constitute the definite double placenta.
The placentas are shed at birth as are those of Sorex and. Erinaceus; they are not resorbed in situ as is that of Talpa.1 The fully ripe placentas, shortly before birth, are in Tupaja connected with the maternal tissue by an area which all along its outer circumference is most easily detached and very loosely connected. Towards the centre, where the principal blood-vessels pass in and out of the placentary structure, the adhesion is more firm.
Foetus of Tupaja at a comparatively late stage of pregnancy are represented in their normal situation in their envelopes and in the uterine horn in figs. 59 and 60. These two were obtained from one and the same uterus. They measure (exclusive of tail) about 27 mm. At birth the foetus has grown to a length of about 40—50 mm.
Manis. Figs. 42—45
This genus, of which I have an extensive collection of uteri that were obtained from Manis javanica (the trengiling or tangiling of the natives), has of late years been investigated with respect to its placentation by Max Weber.1 This fact enables me to restrict myself to a very short notice, the more so as the earliest stages, of which Weber makes no mention, have not yet been studied by myself at all, although they are also well represented in my collection. This, again, has to be reserved for a future publication. In explanation of the figures given on Pl. 12 I may say that fig. 42, which is enlarged twice, was an embryo that had been contained in the uterus of which a portion of the inner surface is represented in fig. 43. This inner surface is characterised by irregular villiferous bands, which become more numerous and more closely approximated as pregnancy advances.
The fœtus and its envelopes is very loosely applied against the maternal surface, outgrowths on the outer layers corresponding to and interlocking with the maternal villiferous bands just noticed.
Sections of these arrangements are figured by Weber.
In the uterus of fig. 43 the embryo of fig. 42 was enclosed in the membranes that are represented in fig. 44. These membranes are peculiar in so far as only a part of the sac appears expanded, a considerable part being more collapsed. Only the expanded portion carries villous bands that interlock with those on the uterine surface. The pregnant horn of Manis carries but one embryo at a time, as was noticed by Weber. For the external shape of the uterus and the very considerable size of the ovaries I may also refer to that publication.
That the aspect of the foetal envelopes is not always that of fig. 44 is shown in fig. 45, which represents a stage of about the same age but of a symmetrical development. The spacious yolk-sac is situated, as was already noticed by Weber, against the lower concavity of this sac. The fœtus enclosed in these envelopes will measure about 20 mm. in length from the vertex to the root of the tail ; towards parturition it will have increased to the size of about 14 cm. from the centre of the skull to the root of the tail.
Having terminated the description of the Spolia nemoris as at this moment they lie before me, I may be allowed to give a summary review of a couple of biological questions in their present stage towards the solution of which I hope in the first place to utilize the material collected.
These questions were already mentioned in the introduction, and have reference to—
The origin and morphological significance of the cell layers constituting the two-layered blastocyst of mammals.
The origin, the minute anatomy, and the morphological significance of the placenta.
Since the very youngest mammalian blastocyst has been studied by means of sections and with the aid of the improved methods of the last decades, our knowledge of those incipient stages has grown very rapidly. For these earliest contributions we are indebted to Rauber,1 van Beneden,2 Lieberkühn,3 and Hensen.1 The rabbit and the bat were more especially employed in these researches ; Heape has added the mole, Selenka several other rodents as well as the opossum, whereas the hedgehog and the shrew were studied by myself. Of late Duval and also Robinson have again investigated the rat and the mouse. Nevertheless, we are at present very far from a consensus of opinion as to the significance and the genesis of the parts in the early didermic mammalian blastocyst.
In his well-known paper on the early development of the rabbit, Ed. van Beneden was one of the first to give a complete set of valuable illustrations of the segmentation of the mammalian ovum and of the consecutive stages between that process and the didermic blastocyst in which the mesoblast begins to make its first appearance.
Several of his figures have since passed into every text-book, although his interpretation, both of the earliest and of the later stages, is not adhered to in the form in which it was originally given. Concerning the earlier stages, Lieberkühn (1. c.) and afterwards Kólliker2 have demonstrated that not only the lower layers, but also the epiblast of the embryo arises out of the inner cell-mass—v. Beneden’s “masse endodermique.” Concerning the later stages, they pointed out that van Beneden mistook (1. c., pl. 5, fig. 7, and pl. 7, fig. 2) for the mesoblast what is in reality the embryonic epiblast. The latter mistake was due to the presence of a trophoblastic layer of flattened cells outside that embryonic epiblast.
As to the development of the hypoblast, van Beneden made out that both in the rabbit and the bat it gradually extends centrifugally around the inner surface of the monodermic blastocyst, the centre of this irradiation being the thicker knob of tissue where the embryo is being shaped.
Similar formation of the hypoblast has been described by v. Beneden and Julin for the bat, by Heape for the mole, by myself for the shrew, and by Selenka for the opossum.
The extension of the hypoblast against the outer wall of the blastocyst is obtained in a different way in the hedgehog, as I have elsewhere described.1 Instead of having to spread out against the inner surface of the wall of the blastocyst, the hypoblast of the hedgehog is from the beginning a solid knob which develops into a closed sac by distension. Further distension goes parallel to further growth of the didermic blastocyst.
The cause of the difference in development of the hypoblast is most probably the ever so much smaller size of the hedgehog’s blastocyst when compared in corresponding phases with that of the rabbit, mole, &c. This is in its turn caused by the fact that the hedgehog’s blastocyst, instead of being located in the uterine lumen, becomes included at a very early stage in the midst of maternal proliferating tissue. (‘Anat. Anz.,’ iii, p. 906.)
In 1892 Dr. Arthur Robinson2 published a paper in which, starting from what he finds in the mouse and the rat, which he has studied for himself, he looks upon the process of hypoblast formation in the rabbit and bat in quite a different light than has been done by former investigators. The process in the hedgehog is, according to bis views, more directly comparable to what he finds in the mouse. He has based on his observations a series of far-reaching theoretical speculations that partly correspond to views propounded by Sedgwick Minot in 1885.3 Robinson concludes that in mammals it is not the hypoblast that spreads against the inner surface of the epiblastic wall of the blastocyst ; but that, on the contrary, the epiblast, at a quicker or slower rate, spreads over the outer surface of a hypoblastic vesicle, which, according to his views, is there from the very first and forms the greater part of the wall of the monodermic blastocyst.
In support of these views the author discusses the existing figures and descriptions of early mammalian blastocysts with considerable ingenuity. A couple of very difficult cases, which I see no possibility of including in Robinson’s speculative attempt, are, however, by him passed over in silence. As such I would, for instance, point out Selenka’s fig. 2, pl. 18, of the opossum (e Studien z. Entwickelungsgesch. der Thiere,’ Heft 4), as compared both to earlier and later stages.
On p.46 of Merkeland Bonnet’s ‘Ergebnisse der Anatomie und Entwickelungsgeschichte’ (vol. ii, 1892), Gr. Born, in referring to Robinson’s paper, recognises that if the views therein contained were confirmed, this would mean a total revolution of our present interpretation of the earlier stages of mammalian ontogeny. Born adds, “an der nothwendigen Nachpriifung der Resultate wird es nicht fehlen.”
Such a “Nachprüfung” can be fully instituted with the aid of the material now in my possession. Already have I examined continuous section series through more than sixty segmentation stages and mono- and didermic blastocysts of Tupaja that had not yet adhered to the uterine wall, and through fourteen preparations of the same early stages of Tarsius.
I will elsewhere fully report about these preparations, but may be allowed now already to assert that they go dead against Dr. Robinson’s speculations, and that I have no doubt that certain peculiarities observed in Tupaja will convince even Dr. Robinson of the fact that the outer layer of the mammalian monodermic blastocyst (i. e. the trophoblast) is not in direct continuity with the hypoblast cells inside of it.
On the other hand, we must recognize in Dr. Robinson’s speculations, as also in the preceding attempt of Minot (1. c.) and Keibel (‘Anat. Anzeiger,’ vol. ii, p. 770), 1 laudable efforts to the solution of a puzzle which the comparison of the holoblastic ova of Mammalia and of the lower Vertebrates and of Amphioxus present to us as yet. For my own part I hold that the principal reason why so many divergent and conflicting views have been consecutively adhered to with respect to the early mammalian blastocyst is this, that the appearance of a cavity in a segmenting ovum has never left room for a doubt whether this cavity could be anything else than a segmentation cavity which, as such, was proclaimed tobe homologous with that of Amphioxus. This homology, I hold, does not exist. It should be remarked that both epiblast and hypoblast, that will build up the embryo, are in the early monodermic stages of the mammals contained inside this cavity; and that we have to expect the real segmentation cavity to arise between epiblast and hypoblast, as also in mammals it actually does later on.
If the space enclosed in the earlier monodermic stages is not the segmentation cavity, then there will be no more a priori difficulties to understand that a great portion of it is afterwards converted into the archenteron. In fact, as little difficulty as that a part of the cubic space inside the shell of a hen’s egg becomes converted into the chicken’s cerebral ventricles.
A comparison with another point in the embryology of the higher Vertebrates will show that the above conclusion about the cavity of the monodermic mammalian blastocyst is less hazarded than might appear at first sight.
Suppose for a moment that the details of the development of the amniotic Vertebrates were absolutely unknown to us, and that we were only fully acquainted with that of the anamnia.
And suppose then some embryologist to teach that the difference between the development of these anamnia and the as yet unknown higher Vertebrates would, for instance, prove to be this, that the latter manage to become suspended for a time in their own body-cavity, he would be in some danger of provoking hilarity, if not worse.
Still we find no difficulty in interpreting the latter phenomenon, thanks to the gradual steps by which embryology has advanced. The segmenting ovum of mammals may thus be said to present the peculiarity, that among the products of the holoblastic segmentation only one or very few cells represent the real embryo; whereas a very considerable number that rapidly expand into a vesicle (against the inner wall of which the hypoblast becomes applied later on, either in one way or another), are segregated at an uncommonly early period in order that they may help to bring about a satisfactory attachment between the blastocyst (which sensu strictiori is as yet enclosed in this early vesicle) and the mother.
Only when the inner cell-mass shows the first traces of differentiation between those elements that will become hypoblast and those that will become epiblast cells, is the stage reached that corresponds to the blastula of Amphioxus ; only then there can be question to look for the homologue of the segmentation cavity. As hypoblast and epiblast are at first firmly pressed together, this segmentation cavity is even then not yet present. The monodermic mammalian blastocyst is thus a pseudo-blastula stage, its cavity is not the real segmentation Cavity, but a cavity which could not fail to arise ever since, for purposes of attachment and nutrition, an extreme case of precocious segregation of certain epiblast cells has come to occur in the mammalian ontogeny. These cells arrange themselves into a vesicle even before the two primary germinal layers of the embryo have differentiated.
There can be no doubt, however, that, phylogenetically, it is the epiblast from which these cells have been segregated ; and this explains the intimate fusion which, after a certain time, obtains between this outer layer and the embryonic epiblast at the periphery of the latter.
If I am right in upholding that the cavity inside the mono-dermic mammalian blastocyst is not the segmentation cavity, and that this blastocyst is only a pseudo-blastula, then we must similarly conclude that it is not a real holoblastic segmentation which the mammalian ovum undergoes. Even the name of tertiary holoblastic, which Rabi proposes to apply to the mammalian ovum (“Théorie des Mesoderms,’ ‘Morph. Jahrb.,’ vol. 15, p. 165), does not yet sufficiently express the fundamental difference by which the mammalian segmentation process is characterised.
There is no shred of evidence that with the disappearance of the yolk, which took place at a comparatively late stage when the mammalian character had already become predominant, the process of segmentation immediately fell back into the lines of the so infinitely more distant alecithal ancestral forms.
A further reason for the distrust with which we may look at this apparently holoblastic segmentation process is the fact that it finally results in the appearance of a tridermic blastocyst with elliptical blastoderm, primitive streak, &c., entirely corresponding to the arrangement of the Sauropsida. So these later stages have not returned to the earlier modes of development, but have continued along the lines laid down by the hereditary transmission of characters that were peculiar to those ancestral forms that possessed a considerable amount of food-yolk.
If the mammalian (pseudo) morula and (pseudo) blastula were indeed comparable with the same stages, i. e. with the true morula and true blastula in Amphioxus and the Amphibians, about one half of the segmentation spheres would represent potential epiblast, and the other half potential hypoblast. Now this is evidently not the case. By far the greater portion of these segmentation spheres gives rise to what will afterwards be not any integral portion of the embryo, but a part of the fœtal envelopes and of the membranous expansion by which the embryo is connected with the mother. Suppose we were able to repeat Roux’s or Chabry’s most important experiments on the partial destruction of one or more of the segmentation spheres with the earliest mammalian stages, then we might predict with great certainty from the data that Rauber, van Beneden, Heape, Selenka, and others have brought to light that only if the mother-cell of the inner cell-mass were attained, the normal development would be interfered with ; and that in the case of other segmentation cells being punctured, only a local defect in the fœtal membranes would ensue. This hypothetical experiment may still further drive home what is meant by the non-homology of the two cases of holoblastic segmentation and of the cavities which arise in these two cases inside the mono-dermic vesicles.
New and valid reasons are thus accumulated for designating the outer layer of precociously segregated epiblast-cells that form the wall of this vesicle by a separate name, which al the same time gives expression to the consideration that adaptation to nutritive conditions of an entirely novel nature has initiated this phenomenon of precocious segregation, simultaneously with the diminution and the final disappearance of food-yolk, a phenomenon that was consequent upon the passage from the Hypotherian to the Eutherian stage.
Already in 18881 have I proposed—and several embryologists, Dr. Robinson included, have since accepted—the name of trophoblast for this outer layer of the mammalian blastocyst.
Only lately2 I have given a fuller definition of the term, which is, however, only in one respect an amplification of the original definition of 1888. Then already (‘Anat. Anz.,’ iii, 510), I remarked that to the trophoblast belonged all those peculiar cellular structures of the mammalian blastocyst which had been indicated by different authors as Reichert’s cells and Rauber’s “Deckschicht “(Kolliker), as “Trager” (Selenka), Ektoderinawulst (Kolliker), horseshoe-shaped proliferation (van Beneden). To this list may yet be added Duval’s “formation ectoplacentaire.”
The amplification of 1893 just alluded to was this, that I not only defined the trophoblast as “the epiblast of the mam-malian blastocyst that does not take part in the formation of the embryo,” but that I added to this, “or of the inner lining of the amnion cavity.”
The difference which obtains between the trophoblast and between the embryonic epiblast contributing to the formation of the embryo and of that inner lining of the amnion cavity, is most distinctly brought out in such mammals as Pteropus, Cavia, Tupaja, and others. Take, for instance, Selenka’s figure of the guinea-pig’s blastocyst,1 Gohring’s of that of Pteropus.2 In these latter figures, we see the epiblastic knob which is enclosed between the trophoblast and the hypoblast of the didermic blastocyst, hollowing out into a cell-mass, of which the upper surface thins out and becomes the epiblastic clothing of the amnion cavity, whereas the lower surface thickens and becomes the epiblast of the blastodermic surface out of which the embryo will be modelled.
I have no doubt that in the cases of Erinaceus and Sorex a similar sharp line of demarcation may be drawn between the epiblast that will develop into the lining of the amnion and between the trophoblast, although here this distinction is not so self-evident as in the preceding cases. And I suspect that even such cases as that of the rabbit will some day admit of a sharper delimitation of these two.
But even where such a sharp delimitation is not as yet always possible in the later stages of the blastocyst, the earlier stages are all the more evident.
The Ornithodelphia are not as yet affected by the causes which determine the differentiation of a special trophoblast in the higher placental Mammalia. In the Didelphia we may hope to find certain transitory stages. Thus the early stages of Phascolarctos, the ovum of which has been described by Caldwell, may be expected to be especially instructive. Already in the opossum Selenka has described the very peculiar proliferation in the outer layer of the early blastocyst (l.c., Heft 4, pl. 20, figs. 2, 5, and), which is no doubt precursory to the ever so much more important proliferations of the trophoblast which occur in most of the higher orders of mammals.
In this paper it has already been noticed how both in Tupaja and in Tarsius, portions of the trophoblast undergo very active proliferating processes preparatory to the placentary fixation of the blastocyst, whereas in my former papers I have described the same activity for Erinaceus1 and Sorex.2
Robinson’s speculations having tended to bring the part that the hypoblast plays in the mammalian blastocyst more into prominence, E. van Beneden has, on the contrary, upheld3 that the inner layer—his “so-called” hypoblast—of the mammalian blastocyst is not homologous with the hypoblast of Amphioxus, but should be regarded as a yolk-envelope and be no longer designated by the name of hypoblast, but by that of lecithophore.
These views, tentatively accepted by Rabi,4 have been combated by Keibel,5 by myself,6 and by others. Also with respect to this question I have no doubt that the material here described will furnish very useful and perhaps decisive data. Decisive, for example, with respect to the question whether mesoblaSt takes its origin out of this hypoblast layer (v. Beneden’s lecitophore), as Bonnet7 and Hubrecht6 have distinctly stated and figured it to do, although others (Keibel,8 for instance) deny this. It is clear that such participation in the formation of the mesoblast is in itself sufficient to invalidate v. Beneden’s considerations about the “lecitophore “and to establish the homology of this layer with the hypoblast of Amphioxus and the lower Vertebrates.
I have myself tried to explain the peculiarities that in mammals also attend the formation of the hypoblast by the suggestion that precocious segregation of part of the hypoblast comes into play and that we have to distinguish a cœnogenetic and a palingenetic hypoblast. This suggestion has been favorably received ; the natural counterpart of it is the above sketched precocious segregation of part of the epiblast. Both are adaptations to similar external conditions.
The origin, the minute anatomy, and the morphological significance of the placenta have been of late inquired into by a considerable number of independent investigators. It may suffice to cite among the more recent ones Duval,1 Strahl,2 Frommel,3 Fleischmann,4 van Beneden,5 Masius,6 Lfisebrink,7 Heinricius,8 Minot,9 Hubrecht,10 and others. Questions that were more particularly entered into are those that concern the fate of the maternal epithelium at the spot where the blastocyst comes to adhere against the uterine surface. In Erinaceus it undergoes changes that are very different from those that take place with it in the rabbit, and different again from what happens with it in the Carnivora. In Sorex the fate of the maternal epithelium is yet more peculiar, considering the fact that an uncommonly marked proliferation of this epithelium precedes its definite disappearance.
Secondly, the question has been much ventilated which part the trophoblast plays in the attachment of the blastocyst. Both in Insectivora (Erinaceus, Sorex, by myself) and in Rodentia (rabbit, mouse, rat, Meriones, Cavia, by Duval) this has been fully inquired into, and overwhelming evidence has been forthcoming to show that this epiblastic layer and no other but this layer contributes in ah unexpected measure to the genesis of the tissues that constitute the placenta.
It may even be said that since the penetration of maternal blood into lacunar spaces of the hedgehog’s trophoblast that are devoid of any vascular endothelium has been described as occurring even at stages as early as the didermic blastocyst,1 and since Duval made his first communication about the rabbit and other Rodents to the Paris Société de Biologie,3—communications that have soon after been worked out in his masterly volume, ‘Le Placenta des Rongeurs’ (Paris, 1889-92),—a conflict of opinion has arisen about the real nature of the placenta, in which on one side are a majority of the above-cited German anatomists, and on the other the two authors just named and also E. van Beneden with reference to the bat (‘Comptes Rendus de la Société de Biol.,’ vol. v, Novembre, 1888), and J. Masius, his pupil, with reference to the rabbit (1. c.).
The question centres in the way in which the osmotic interchange between the maternal and the embryonic blood comes about, influenced as it is by preparatory processes that take place in those regions where the trophoblast of the blastocyst comes in contact with the inner lining of the uterus.
Now this phenomenon is easy enough to understand in the horse, the pig, and several other mammals on which the researches of Turner, Ercolani, &c., have already years ago thrown a flood of light.
We find there what we find repeated in two of the genera which are treated of in this paper, viz. Manis and Nycticebus. The outer layer of the blastocyst acquires numerous villiferous processes that are vascularized and fit into vascular crypts of the maternal wall, out of which they are retracted at birth with the greatest facility. In Nycticebus the two epithelia, both the embryonic and the maternal, remain intact, and the osmotic interchange takes place through two cell-layers of different origin and of different physiological significance (phylogenetically).
As soon as the complications in this arrangement commence to make themselves felt, which are so varied and so characteristic in the different and so-called “deciduate” orders of mammals, a clear insight is much less easily obtained. Partly because as yet only a restricted number of genera has been examined sufficiently in detail; partly because when such investigation has taken place the different observers do not always concur in the interpretation of the phenomena which present themselves on examining the microscopical preparations of the same species.
A significant cell-layer is by the one declared to be maternal, by the other to be of embryonic origin. Maternal blood is by the one said to be enclosed in vascular spaces, that never lose their real character of further extensions of capillary vessels, whereas the other pretends that the maternal blood penetrates sometimes at a very early, sometimes at a later stage of the ontogenesis into lacunar spaces that are wholly surrounded by tissue that is exclusively of embryonic origin.
Duval very tersely expresses the latter view, of which he is himself one of the staunchest advocates, as follows :—” Le placenta représente à son origine, une hémorragie maternelle, circonscrite ou enkystée par des éléments fœtaux ectodermiques.” The fact that certain interpretations based on older researches, that could not yet profit by the modern technical improvements, have been adopted in the text-books, gives a long vitality to views which would most probably be soon abandoned if the problem were now-a-days brought forward for the very first time. Similarly, generalisations that were based on incomplete data, although fully justified at the time when they were made, are now found to obstruct the way to a certain extent.
One of the mammals that will facilitate the real understanding of the method according to which the very simple manner of fcetal interchanges above alluded to has been converted into the more complicated placentary structures, is the mole. Some years ago I called attention to the fact (‘Quart. Journ. Microsc. Science,’ vol. xxx, pp. 346 and 388) that here, too, embryonic villi that cover the foetal envelopes are easily drawn out of their sheaths at birth, and that no afterbirth is shed, although the animal has a discoid placenta, which up to lately was held to mean that it was also deciduate. I then expressed the opinion that not only the mole is not deciduate, but that even embryonic tissue is left behind against the uterine surface, and is gradually resorbed in situ.
According to the patient investigations made by Mr. Vernhout, a pupil of the Utrecht Zoological Laboratory, which are at present in the press, this is actually the case. Mr. Vernhout has cleared up the early details of the mole’s placentation, and comes to very different conclusions from those of Strahl.
We may say that in the mole the epithelial connection, as it was described above for Nycticebus and others, is a phase that is very rapidly passed over, and that it is followed by the application of a trophoblastic cell-layer against the maternal epithelial layer. According to Mr. Vernbout’s investigations, based upon preparations which I have myself repeatedly had occasion to compare with the drawings which he is about to publish, the maternal epithelium is very rapidly destroyed, the trophoblast now becoming a pseudo-epithelium by which the denudated mucosa and its deepening crypts are covered. Into these crypts, which are in fact of embryonic origin, the allantoic villi penetrate and are withdrawn out of them at birth, the trophoblastic pseudo-epithelium, and the further derivates it has given origin to, remaining in connection with the maternal tissues.
I hold this to be not a secondary modification which has arisen among mammals that were already frankly deciduate, but, on the contrary, a more primitive developmental phase. In very many cases it may have preceded that more complete arrangement in which the uterus, after having expelled the fœtus, also rids itself (be it even at the cost of some of its own elements—rapidly renovated after parturition) of the growths (afterbirth) by which the embryo has succeeded to obtain so firm a hold on the maternal sanguiniferous tissues.
If we look at the Carnivora, at the bats, the rodents, the Primates, and the Insectivora, we find their more complicated placentary structures to belong to very divergent types. In the latter order there is no common type, but a different one for nearly every genus. The shrew, the mole, the hedgehog, and the Tupaja are all most incredibly divergent with respect to their placentary arrangements. Only when the comparative investigations shall have covered a more considerable number of different genera, the time for new theoretical generalisations will have arrived.
Towards the accumulation of material that would be thus available I hope the Spolia Nemoris here described may contribute.
EXPLANATION OF PLATES 9, 10, 11, & 12,
Illustrating Professor A. A. W. Hubrecht’s paper, “Spolia Neinoris.”
ov. Ovary, lig. Uterine ligament. If. Muscularis of the uterine wall. m. Mucosa of the uterine wall. R. Hollow recesses clothed with epithelium in the chorion of Nycticebus. ap. Apertures by which these open to the exterior, amn. Amnion, u. Umbilical cord. V. Chorionic villi of Nycticebus. cr. Crypts clothed with epithelium, in which these villi fit. gl. Uterine glands.
All figures natural size.
FIG. 1.—Tarsius spectrum. A pregnant uterus in the latest stages. In Fig. 1 the barren horn of the uterus, with coiled oviduct and ovary, are yet visible on the top of the swelling that contains the fœtus. The other ovary protrudes in the left lower border of the figure. At the right lower border the uterine wall shows a rupture ; here the vagina formed its continuation.
Utr. Mus. Cat. n°-Tarsius 10.
FIG. 3.—Tarsius spectrum. Earlier phase of pregnancy. One ovary (ou.) visibly more considerably swollen than the other.
Utr. Mus. Cat. n°’ Tarsius 11.
FIGS. 3—5.—Three uteri of Nycticebus tardigradus. Figs. 3 and 5 front views. Fig. 4 viewed from above to show the peculiar shape of the uterine horns. In the latter figure the vagina and the two ligamenta rotunda are bent forwards from under the horns. Ovaries partly hidden from view by fold, including oviduct. Fig. 5 is the stage furthest advanced ; the fully ripe fœtus reaches up to four times this size.
Fig. 3.—Utr. Mus. Cat. n° Nycticebus 6.
Fig. 4. — Utr. Mus. Cat. n°Nycticebus 7.
Fig. 5.— Utr. Mus. Cat. n°Nycticebus 56.
FIGS. 6a and 6b.—Galeopithecus variegatus. The double uterus in a very early stage of pregnancy. 6 a seen from behind, 6 b seen from above. The two halves of the uterus open out into the vagina by separate canals and openings. There is no median portion in common.
Utr. Mus. Cat. n°’ Galeopithecus 3.
FIGS. 7 a and 7 b.—The same, in a somewhat later stage of pregnancy.
Utr. Mus. Cat. n°’ Galeopithecus 13.
FIGS. 8 a and 8i.—The same, with one of the uteri already very markedly swollen.
Utr. Mus. Cat, n°. Galeopithecus 27.
FIGS. 9a and 9b—The same, in a later stage.
Utr. Mus. Cat. n°. Galeopithecus 18.
FIGS. 10a and 10 b.—The same, with the indication of very much widened blood-vessels in the uterine wall. 10 a seen sideways, 10 b seen from below.
Utr. Mus. Cat. n°. Galeopithecus 16..
FIG. 11.—Side view of a pregnant uterus of Galeopithecus, at nearly full term ; the blood-vessels in the uterine wall yet more prominent.
Utr. Mus. Cat. n°. Galeopithecus 14.
FIGS. 12—16.—Five uteri in early stages of pregnancy of Tupaja javanica.
Utr. Mus. Cat. n°3’ Tupaja 251, 62, 254,17, 39.
FIG. 17.—Pregnant uterus of Tupaja at full term, both halves containing a fœtus, the right placenta of the left fœtus and the left placenta of the right fœtus being visible as a reniform thickening in the uterine wall. The other placentas are situated quite symmetrically on the opposite side, invisible here.
Utr. Mus. Cat. n°-Tupaja 170.
All the figures (with the exception of Figs. 20, 24, and 25) natural size. Colour as shown by spirit specimens.
FIG. 18.—Tarsius spectrum. Fully developed fœtus folded together in fœtal membranes with discoid placenta, viewed from above, on the left side of the drawing. The placenta is actually attached to the maternal tissue only in the central angular spot.
Utr. Mus. Cat. n°-Tarsius 10.
FIG. 19.—The same, seen in profile to show the relative height of the placenta.
FIG. 20.—Tarsius spectrum. Part of the uterine wall after removal of the fœtus. Umbilical cord and placenta in situ. The latter cut longitudinally. Enlarged f.
Utr. Mus. Cat. n°’ Tarsius 15.
FIG. 21.—The same, as seen from below before the placenta was cut in two.
Utr. Mus. Cat. n°. Tarsias 15.
FIG. 22.—Highly pregnant uterus of Nycticebus, with only the muscularis peeled off.. Cf. Figs. 30-32, 52.
Utr. Mus. Cat. n°. Nycticebus 24.
FIG. 23.—Another pregnant uterus of Nycticebus, with three incisions in the’ uterine wall. Two triangular flaps of muscularis and mucosa are folded backwards and reveal the fœtus enclosed in its villiferous envelope. Cf. Figs. 31, 32, 50, 51.
Utr. Mus. Cat. n° Nycticebus 23.
FIG. 24.—Galeopithecus variegatus. Pregnant uterus, opened opposite to the placenta. Embryo in amnion. The yolk-sac has been removed, together with the portion of the uterine wall. Enlarged twice.
Utr. Mus. Cat. n°’ Galeopithecus 18.
Flo. 25.—Placentary area of the same, enlarged three times, after removal of the embryo.
Utr. Mus. Cat. n°. Galeopithecus 18.
FIG. 26.—Another uterus of Galeopithecus, in which the wall opposite ‘the placenta has also been removed, but in which the fœtal membranes, &c., are as yet all of them in situ. The blood-vessels on the yolk-sac are clearly visible. To the right of the figure the section of the uterine wall has passed through a portion of the placentary region.
Utr. Mus. Cat. n°-Galeopithecus 19.
FIG. 27.—The same stage as that of Fig. 26, after the fœtal envelopes have been opened and turned over (yolk-sac and amnion) to the right. The embryo is removed ; the placenta is risible.
Utr. Mus. Cat. n°’ Galeopithecus 19.
FIG. 28.—A similar stage, peeled out of the uterus. The placenta is partly visible on the left. Thé yolk-sac has been cut and turned over to the right, the embryo is yet enclosed by the amnion.
Utr. Mus. Cat. n°’ Galeopithecus 1.
FIG. 29.—Uterus of Galeopithecus at full term, opened. Theripefœtus is attached by the umbilical cord to the discoid placenta, which presents a smooth surface, continuous with that of the uterine wall in which it is implanted.
Utr. Mus. Cat. no> Galeopithecus 17.
Figs. 30—33, 35, 36, and 41, natural size. Figs. 34 × 3, 37 and 38 × 27, 39 and 40 × 16.
FIG. 30.—Nycticebus tardigradus. The same uterus as that of Fig. 22. The flaps of the muscularis in the same position ; mucosa opened ; villiferous chorion inside this opened likewise; amnion partially removed.
Utr. Mus. Cat. n°. Nycticebus 24.
FIG. 31.—Uterus of Nycticebus in somewhat earlier stage of pregnancy, opened by a circular incision. Muscularis and reticular mucosa have here been left in their natural connection, and the portion of the uterine wall that is here bent to the left has been removed from the subjacent villiferous chorion without any effort of traction.
Utr. Mus. Cat. n°’ Nycticebus 84.
FIG. 32.—A similar stage of the same specimen, but in which not only the uterine wall but also the fœtal envelopes have been opened and have also been folded back. Embryo removed.
Utr. Mus. Cat. n°. Nycticebus 45.
FIG. 33.—A ring-shaped section of a Nycticebus uterus, nearly at full term. The embryo alone has been removed. The umbilical cord is seen to divide into a number of vasiferous strands, attached to the inner surface of the chorion. The fœtal envelopes (with the exception of the amnion, which has been removed with the fœtus) have been left in their natural position.
Utr. Mus. Cat. n°. Nycticebus 41.
FIG. 34.—The inner surface of the chorion enlarged three times, showing finely ramifying blood-vessels, both afferent and efferent, the two of different colour in the preserved specimens. Chorionic recesses (cf. Figs. 39 and 40) form conspicuous round projections inwards. The radiate spots correspond to the chorionic villi present on the opposite side.
Utr. Mus. Cat. n°’ Nycticebus 41.
FIG. 35.—Nycticebus fœtus, wholly enveloped by the villiferous chorion, very shortly before birth. Between the villi the apertures (ap.) of the chorionic recesses (cf. Fig. 39) are visible to the naked eye. To the right the villi are larger, but also more flattened and wider apart.
Utr. Mus. Cat. n°-Nycticebus 34.
FIG. 36.—The same Nycticebus embryo of Fig. 30, to show its attachment by means of the umbilical cord (a.) to the chorionic envelope, which is partially turned inside out.
Utr. Mus. Cat. n°. Nycticebus 24.
FIGS. 37 and 37 a.—Three chorionic villi of Nycticebus as seen from above, enlarged × 27. They were taken from the specimen of Fig. 30, and are seen to be multilobulate.
Utr. Mus. Cat. n°. Nycticebus 24.
FIG. 38.—The prominent network of the mucosa in which the chorionic villi fit. Also taken from the same specimen and enlarged ×27.
Utr. Mus. Cat. n°. Nycticebus 24.
FIG. 39.—Transverse section of a portion of the chorion of Nycticebus. Blood-vessels are red. Epithelial covering of chorionic villi here and there thickened, more especially on the tops of the villi. Chorionic epithelium continuous in the round and flattened recesses (22.) that open out in the extra-chorionic space by the apertures (ap.).
Utr. Mus. Cat. n°. Nycticebus 24.
FIG. 40-—Another section of the chorion of Nycticebus, but with the portion of the uterine wall against which the chorion is applied in situ. The numerous indentations and reticularly; arranged spaces into which the chorionic villi fit are also covered by an epithelium which is generally somewhat flatter than that of the chorion. The maternal as well as the fœtal blood-vessels are indicated by a red colouring. It can here be seen that the separation which in Figs. 22 and 30 was brought about between muscularis and mucosa must have been facilitated by the intervening glandular region here indicated. The chorionic recess in this figure protrudes further inwards than those of Fig. 39.
Utr. Mus. Cat. n°’ Nycticebus 45.
Flo. 41.—One of the two compartments of the pregnant uterus at full term of Tupaja javanica (cf. Fig. 17), opened by a longitudinal incision. The fœtus was cut in two by this operation, the one half that is figured in outline fitting in the uterine segment to which it remains attached. The vessels of the umbilical cord (which passes towards the dorsal side of the fœtus) are there seen to divide into four principal tracts, two for each placenta. The placenta which was situated to the right of the fœtus is figured in the lower, that which was situated to the k.t of it in the upper segment. The latter has thus to be placed in situ by revolving downwards arouijd its base line by 180°. The cut vessels at the top of the figure will then be seen to become continuous with those at the bottom of it.
Utr. Mus. Cat. n°. Tupaja 258.
All the figures natural size with the exception of Figs. 42, 46, 55 and 56, which are enlarged twice.
FIG. 42.—Early embryo of Manis javanica prepared out of the fœtal envelopes that are represented in Fig. 44. Enlarged X 2.
Utr. Mus. Cat. n°. Manis 29.
FIG. 43.—View of the inner surface of a preguant uterus of Manis javanica that contained the fœtus and fœtal envelopes of Figs. 42 and 44. Villosities on the inner uterine surface united into irregular bands.
Utr. Mus, Cat. n°-Manis 29.
FIG. 44.—Fœtal envelopes of Manis javanica that contained the fœtus which is represented (enlarged twice) in Fig. 42. These fœtal envelopes were obtained intact (after the uterus had been opened) by simply floating them out. The fœtus was contained in the left part. The twisted projection stretching to the right was devoid of villosities, and measures about twice the length of the villiferous portion in which the fœtus and yolk-sae were found. It is an example of an asymmetrical arrangement of the fœtal envelopes in contrast to those of Fig. 45.
Utr. Mus. Cat. n°* Manis 29.
JIG. 45.—Manis javanica. Embryo of about the same age in its fœtal envelopes, the latter more symmetrically developed than in Fig. 44. The streaks and bands on the surface corresponding to villous bands on the uterine wall are clearly visible. The yolk-sac is internally applied against the lower concave surface.
Utr. Mus. Cat. n°’ Manis 71.
FIG. 46.—Tarsius spectrum. Young embryo removed out of its enveopes, seen in profile. Enlarged f.
Utr. Mus. Cat. n°. Tarsius 11.
FIG. 47.—Nearly ripe fœtus of Tarsius spectrum enclosed in all its membranes. The discoid placenta is here visible at the top. The only point of adhesion with the uterine wall is found in the midst of this placentary disc (cf. Figs. 18 and 19).
Utr. Mus. Cat. n°. Tarsius 10.
FIG. 48.—Fœtus of Tarsius of about the same age removed out of its fœtal membranes.
Utr. Mus. Cat. n°. Tarsius 15.
FIG. 49.—The fetal membranes of aTarsius at full term after the removal of the fetus. Discoid placenta and umbilical cord distinct.
Utr. Mus. Cat. n°. Tarsius 101.
FIG. 50.—Fœtus of Nycticebus tardigradus enclosed in its villiferous chorion. Obtained by very gently ‘turning upside down the opened uterus (Fig. 51) in which it was enclosed.
Utr. Mus. Cat. n°’ Nycticebus 84.
FIG. 51.—One half the uterus of Nycticebus in which the fetus of Fig. 50 has been enclosed. View of the inner surface.
Utr. Mus. Cat. Nycticebus 84.
FIG. 52.—The mucosa of Nycticebus of the stage represented in Figs. 22 and 30, peeled off from the muscularis and seen from the inside.
Utr. Mus. Cat. n0, Nycticebus 24.
FIG. 53.—Nycticebus fetus in all its envelopes, the latter being more folded than in Fig. 50.
Utr. Mus. Cat. n”-.Nycticebus 23.
FIG. 54.—A later fetus of Nycticebus prepared out of its envelopes, part of which are still in connection with the umbilical cord and visible above the head of the fetus.
Utr. Mus. Cat. n’- Nycticebus 54.
FIG. 55.—The villiferous chorion in a very late stage of pregnancy. Enlarged X 2. To the right the villi are more flattened (cf. Fig. 35).
Utr. Mus. Cat. n°. Nycticebus 34.
FIG. 56.—The reticulated mucosa of a similar late stage of pregnancy. Enlarged x 2.
Utr. Mus. Cat. n°. Nycticebus 34.
FIG. 57.—Embryo of Galeopithecus removed from its envelopes, front view. The severed umbilical cord is seen protruding between the claws.
Utr. Mus. Cat. n°. Galeopithecus 54.
FIG. 58.—Much younger embryo of the same, viewed in profile.
Utr,Mus. Cat. u°. Galeopithecus 19.
FIG. 59.—Fœtus of Tupaja javanica in its half of the uterus. This latter was slit open longitudinally, and the left placenta visible. The right placenta is hidden from view by the embryo.
Utr. Mus. Cat. n°’ Tupaja 302.
FIG. 60.—The same, the fœtus from the other half of the same uterus. The head of the fœtus is seen to be directed distally towards the vagina.
Utr. Mus. Cat. n°. Tupaja 302.
While correcting this proof, new arrivals have again increased this total to 1072.
It should be here noted that I have on more than one occasion heard it reported ‘by sportsmen and natives that for the Indian deer, periods of heightened and lessened sexual activity do exist. I will by no means generalise any further than my acquaintance with the species here investigated will allow me to do.
Renson, ‘Contribution à l’embryologie des organes d’excrétion des oiseaux et des mammifères,’ Bruxelles, 1883, p. 37.
C. K. Hoffmann, “Die Bildung des Mesoderms, &c.,” ‘Verb. v. d. Kon Akad. v. Wetenschappen te Amsterdam,’ 1883, p. 2.
J. v. Erp, Taalman Kip, ‘De ontwikkeling der Müllersclie gang by de zoogdieren,’ Dissert, inaug., Utrecht, 1893, p. 77.
Cf. a preliminary notice in the ‘Procès Verbaal van de Koninkl. Akademie van Wetenschappen te Amsterdam,’ Zitting van 2 April, 1892,
Of this species I have obtained but very few specimens in East Java, and no pregnant uteri. Although no specific determination was ever made by those who so kindly collected and preserved the uteri at present available, I have no doubt that they all belong to the only species which is known to occur in the islands from which my collections have come (Sumatra, Banka, and Borneo), viz. Nycticebus tardigradus.
A. Milne Edwards et A.Grandidier, ‘Histoire Naturelle des Mammifères de Madagascar,’ Paris, 1875.
Turner, “On the Placentation of the Lemurs,” 1 Philosophical Transactions of the Royal Society,’ 1876, p. 569, pls. 49—51.
‘Studien z. Eutwickelungsgeschichte der Tiñere,’ Heft 4, “Das Opossum,” p. 136.
”The Placentation of Erinaceus europæus, &c.,” ‘Quart. Journ. Mier. Sei.,’ vol. xxx, 1889, p. 382.
‘Studien z. Entwickeluiigsgeschiciite der Tiñere,’ Heft 5, pl. 35, fig. 11 ; pl. 36, fig. 5.
“Mémoire sur les formes cérébrales propres à différents groupes de mammifères,” ‘Journal de Zoologie,’ vol. i, 1872.
‘Procès Verbaal der Koninkl. Academie van Wetenschappen te Amster. dam,’ 27 Mei, 1893.
Cf. ‘Quart. Journ, Mier. Sci.,’ vol. xxx, p. 346.
‘Zoologische Ergebnisse einer Reise nach Niederlândisch Ost-Indien,’ vol. ii, 1891, pp. 1—118, pls. i—ix.
“Die erste Entwickelung des Kaninchens,” ‘Sitzungsberichte der Leipziger Naturforschenden Gesellschaft,’ 1875, p. 103.
‘Bulletin de 1’Acad. de Belgique,’ t. 60, 1875, p. 686 ; five years later followed by “La formation des feuillets chez le lapin,” ‘Archives de Biologie,’ vol. i, 1880.
“Deber die Kleimblátter der Säugethiere,” ‘Gratulationsschrift Nasse,’ Marburg, 1879.
“Beobachtungen über die Befruchtung und Entwickelung der Kaninchen und Meerschweinchen,” ‘Archiv f. Anatomie und Entwickelungsgescbicbte,’ Bd. i, 1876.
” Die Entwickelung der Keimblätter des Kaninchens,” ‘Zoolog. Anzeiger,’ iii, 1880, pp. 370 and 390.
‘Anat. Anzeiger,’ Bd. iii, pp. 511, 906 ; and ‘Quart. Journ. Mier. Sei.,’ vol. xxx, p. 291.
‘Quart. Journ. Mier. Sei.,’ vol. xxxiii, p. 369.
‘Buck’s Reference Handbook of Med. Sciences,’ i, 528, 1885 ; and ‘American Naturalist,’ September, 1889 ; also ‘Human Embryology,’ 1893, p. 107.
I cannot admit with Keibel the possibility of a “Wachsthumsenergie derjenigen Zellen des Eies welche friiher den Dotter umwuchsen,” which would be unchecked for millions of generations after the disappearance of the yolk, and which is by him meant to explain certain formative processes in the blastocyst.
’ Anatomischer Anzeiger,’ July, 1888, p. 510.
‘Prooes-verb. van de Kon. Akad. van Wetenschappen te Amsterdam,’ 27 Mei, 1893.
’ Studien zur Entwickelungsgesch. der Thiere,1 Heft 3, pl. 12, figs. 13— 15, 73.
Ibid., Heft 5, pl. 41, figs. A—C, 1; 2, 4, and 6.
‘Quart. Journ. Mier. Sci.,’ vol. xxx.
Ibid., vol. xxxi.
’ Anatomischer Anzeiger,’ iii, p. 713.
” Théorie des Mesoderms,” ‘Morphol. Jahrb.,’ Bd. xv.
’’ Zur Entwickelungsgesch. der Chorda bei den Saugern,” ‘Archiv far Anat. und Physiol. Anat.,’ Abth., 1889.
”Devélopment of the Germinal Layers of Sorex vulgaris,” ‘Quart. Journ. Mier. Sci.,’ vol. xxxi, 1890.
”Beitrâge z. Embryologie d. Wiederkâuer,” 1 und 2, ‘Archiv für Anat. und Physiol.,’ Anat. Abth., 1884, p. 170, and 1889.
” Ueber die Entwickelungsgesch. des Schweines,” ‘Anat. Auz.,’ vi, 1891, and Schwalbe’s ‘Morph. Arbeiten,’ Bd. iii, 1893, S. 69.
M. Duval, “Le Placenta des Rongeurs,’ Paris, 1889-93.
H. Strahl, “Untersucliungen ü ber den Bau der Placenta,” I—IV, ‘Arch. f. Anat. u. Physiol.,’ 1889, 1890. V. Anat. Hefte von Merkel u. Bonnet, 1892.
R. Frommel, ‘Ueber die Entwickelung der Placenta be.i Myotus murinus,’ Wiesbaden, 1888.
A. Fleischmann, ‘Embryologische Untersucliungen,’ Hefte 1—3, Wiesbaden, 1889-93.
E. v. Beneden, ‘‘De la formation et de la constitution du placenta chez le Murin,” ‘Bull. Acad. roy. Belg.,’ 3e ser., t. 15, 1888.
J. Masius, “De la genèse du placenta chez le lapiu,” ‘Archives de Biologie,’ vol. ix, 1889.
F. W. Liisebrink, “Die erste Entwickelung der Zotten in der Hundeplacenta,” Anat. Hefte von Merkel u. Bonnet, ii, 1892.
Heinricius, “Ueber die Entw. u. Struct, d. Placenta beim Hunde,” ibid. “bei der Katze,” ‘Arch. f. mikr. Anat.,’ Bde. 33 u. 37.
C. S. Minot, “Uterus and Embryo,” ‘Journal of Morphology,’ ii, 1889.
Hubrecht, “Erinaceus,” ‘Quart. Journ. Mier. Sci.,’ xxx, 1889 ; “Sorex,” ibid., xxxv, 1894 ; and ‘Verhandel. k. Akad. v. Wetensch. Amsterdam,’ 2e Sec., vol. iii, 1893.
Hubreclit, ‘Kleimblatterbildnng und Placentation des Igels,” *Verhandlungen der Anat. Gesellsch. ; Versammlung zu Würzburg,’ Mai, 1888 ; ‘Anat. Anz.,’ iii, p. 512 ;.and “The Placentation of Erinaceus europæus,” ‘Quart. Journ. Mier. Sci.,’ vol. xxx.
‘Comptes-rendus de la Société de Biologie,’ Mars et Juillet, 1887 ; Octobre et Novembre, 1888, vols, iv et v.