GENERAL CONSIDERATIONS
To the above description of Actinophrys, it will not be out of place to add a few general reflections, and in the first place to ask what systematic position it is entitled to take.
When compared with the simplest known forms of animal life, it appears clear that Actinophrys is most closely allied to Amoeba and the Rhizopoda of Dujardin, who himself agrees in this view, and considers that it differs from them only in the uncommon slowness with which the tentacles are moved. In fact Actinophrys, like Amœba, Gromia, See.., consists of a perfectly homogeneous, everywhere contractile substance, without any trace of structure, and having in precisely the same way processes on the surface of an ephemeral nature and of various forms. The granules also of Actinophrys and its clear spaces have their analogues in the granules of Amoeba and Gromia and in the vacuoles of Amœba, Arcella, Trinema, and Gromia. And just in the same way an Actinophrys artificially divided by Eichhorn, finds its exact counterpart in an Amœba princeps, the same observation being made also by Dujardin. It must be confessed that, notwithstanding this correspondence, Actinophrys exhibits a great peculiarity in its mode of taking nourishment. But is it ascertained, it may be asked, that the Amoebae and Rhizopoda take in their food in any other way ? By no means; much rather does it seem, to the author at least, from all that is known as to the mode of feeding in those creatures, to be indicated, that it is precisely similar to that which obtains in Actinophrys. We have only to refer to what Dujardin remarks with respect to Amœba (Infus., p. 228 et seqi) to see that he was very near the discovery of the remarkable proceeding witnessed by the author in Actinophrys. Referring to the circumstance that in the first place there is in Amœba neither mouth nor intestine, and secondly, that, nevertheless, Naviculae, Closteria, fragments of alga?, and other nutritious particles occur abundantly in its interior, having been admitted at any part of the surface at will—it may be held as an established fact, that the admission, digestion, and rejection of the food is effected in Amoeba precisely in the same way as in Actinophrys. Dujardin, moreover, himself, although he assumes that the Amœbæ are nourished by means of absorption, and that the nutritious matters above mentioned, enter them only by accident, is not inclined to deny that they do derive nutriment from the articles thus included; adding (p. 229)—‘Si toutefois on voulait prétendre, que ces corps étrangers sont entrés par une bouche, et sont logés dans des estomacs, il faudrait admettre, que cette bouche sest produite sur unpoint quelconque, et á la volonté de l’Amibe, pour se refermer et disparaître ensuite, (this recalls Ehrenberg’s expression (p. 128), that the true mouth of the Amœba opens only in the act of swallowing and rejection,) tandis que les estomacs eux-mêmes, dépourvus de membrane propre, se creuseraient indifféremment çà et là au gré de l’animal, pour disparaître de même; dans ce cas les mots seuls seraient différents et l’explication des phénomènes resterait encore celle, que j’ai donné.’ The latter is by no means credible, and it is rather to be asserted that it is not by chance, but by will (sit venia verbo) that the food enters the body in the Amœba. What holds good in Amœba may also be supposed to be the case in the closely-allied Rhizopoda, which, although they have no vestige of a mouth, nevertheless contain Infusoria and Bacillariæ, as has been seen by Dujardin in Areella vulgaris (p. 247) and Euglypha tuberculata (p. 251), and by Ehrenberg in Difflugia enchelys (p. 132) and Arcella vulgaris (p. 133), where even it is remarked, that the latter takes in Indigo, and that in feeding, a spot in the interior of the soft body—from time to time opens and closes—of which spots also two are frequently present.
Relying upon all this, the author is of opinion that Actinophrys belongs to the same group with Amœba and the Rhizopoda of Dujardin, and to which group the latter name seems most appropriate. Distinct families would be formed of the Amœbæ, the species of Actinophrys, to which probably also the genus A cine ta would belong; and of those provided with shells, which again might be divided into those with a simple body (Areella, Difflugia, Gromia, &c.) and those with a simple semi-divided body, the Polythalamia (Miliola, Vbrticialis, &C.). The character of these Rhizopoda would in part be that already given by Dujardin: a structureless body of a homogeneous, contractile substance, without mouth, intestine, or other organs, with mobile processes. Reception of food at any part of the surface of the body, by a retraction of the substance and the introduction of the morsel into the interior; digestion of the aliment in spaces temporarily formed for the purpose, and expulsion of the remains at any spot at will. Propagation by fission ? by germs ?
Having thus shown the alliance of Actinophrys with Arrurba, Gromia, &c., the position of the thus constituted Rhizopodous group with respect to the rest of the lower animals remains to be considered. The first question which here arises is, whether this group is to he placed with the Infusoria, or should constitute an independent class. The answer is difficult, since the structure of the Rhizopoda and Infusoria is, it must be regretted, not yet so clearly made out in all points as to admit of a certain comparison between them. The author starts with the proposition that the Infusoria (from which he excludes the Rotifera, and the Bacillaria, Volvocina, and Closterina belonging to the vegetable kingdom) all without exception consist of a single cell. He is of opinion that what he had shown to be the case in the Gregarince,* holds good of all the true Infusoria, as has been shown in the most convincing way by Siebold in his Comparative Anatomy. In this view all the Infusoria consist as it were of a cell, which in the one case is entirely closed (Gregarina, Opalina, Euglena,† &c.); and in the other possesses a mouth or even two openings. No one who examines with sufficient attention an Opalina, Bursaria, Nassula, Sec., can longer entertain the smallest doubt as to this. He will find for the most part a contractile and structureless membrane furnished with cilia, frequently partially contractile cell-contents with granules and vacuoles, and almost always an homogeneous, frequently curiously formed nucleus.
This point being once established, it may be asked, in the second place, Can the Rhizopoda be likened to a cell ? At first sight the answer would appear to be in the negative, seeing that they (Amoeba, Actinophrys, &c.) have no distincttunic equivalent to a cell-wall, and, at least many of them, no cell-nucleus. But it must be inquired, Is this sufficient to deprive them of the title of cells? With respect to the nucleus, it really appears to be present in some of them (vid. Ehrenberg’s figures), and where it is wanting, as in Actinophrys, whose nuclear and vesicular internal substance above described can here hardly be so regarded, a true nucleus may have existed at an earlier period, and be absent only in the full grown animal; or again it may be entirely wanting, and still the animal regarded as a cell. The former supposition is highly credible, the same thing taking place in many cells (human blood-corpuscle, &c.); and with respect to the latter, it may be remarked that although in the higher animals the nucleus is a constant element in the cell, it is still not proved, that, speaking generally, there cannot be a cell without a nucleus, that is to say vesicles, which otherwise in all respects as to growth, reception and rejection of nutriment, movement, increase, &c., behave exactly as do cells. It may here be stated that certain Infusoria, which on account of their great resemblance to others, distinctly unicellular, must be taken to be altogether of a like nature, nevertheless have no nucleus. With respect to the membrane, it may be regarded as certain that there are cells with a membrane of such extreme tenuity as to be hardly distinguishable from the contents; thus the author observed in blood corpuscles of the embryo chicken noticed in the act of division, that when pressure was made upon them, the two halves became separated, and without any escape of colouring matter, were again formed into perfect cells. The blood corpuscles of the Frog under pressure behave very nearly like the soft substance of the filaments of Actiaophrys, the processes of Amœba, Gromia, &c. In the second place, it is to be remarked that there are cells, in which at a later period all difference between the membrane and the contents disappears—for instance, the elements of the smooth muscles in the higher animals—what are termed by the author fibrecells. Which of these possible conditions, as concerns membrane and nucleus, obtains in the Rhizopoda, the author is unable to answer, not knowing with certainty whether they are to be regarded exactly in the light of cells or not, but he goes on to remark that their other relations are not opposed to the notion that they may be simple cells; such as their structureless homogeneous contents, its contractility, and the vacuoles in it, resembling in all respects the contents of the body in the unicellular Infusoria; then the simplicity of their form and mode of taking food, so closely resembling the way in which the Infusoria introduce a morsel into their parenchyma and there digest it. Certainly the presence of a cell-membrane is scarcely reconcilable with the circumstance that the body is capable of admitting a morsel of food at any part of the surface, but partly, it is not indispensably necessary to assume that such exists in the fully developed Actinophrys, and partly also it is by no means wonderful that a membrane, in consistence almost the same as the rest of the parenchyma, should be capable of being torn and of reuniting. To leave, however, this region of hypotheses and possibilities, it may at all events be stated that the notion that the Rhizopoda are of a nature similar to simple although modified cells, has especially this to recommend it, that there is little else to be made of them. It cannot be admitted that they consist of a whole aggregation of cells, and as little is it to be supposed that they are simply a mass of animal matter without further distinction, as it were, an independent living cell contents. And the less can this supposition be entertained, because, according to all recent investigations which have proved cells to be the elementary parts of the higher animals and plants,—as the initial point for further development (ova, spores, &c.), as the simplest form of vegetable organisms (Closterium, Navicula, unicellular Algae, &c.), we cannot in the animal kingdom also, but regard the unicellular animal as the simplest form. On this account it seems provisionally, best to consider the Rhizopoda as peculiarly modified simple cells—which probably may have a membrane, but in the mature condition at least, to all appearance have no nucleus, and to arrange them together with the other Infusoria in the class of Unicellular animals.
In conclusion, the author adds a few words respecting the contractile substance of Actinophrys and the Rhizopoda in general. He is induced the more to do this by a very interesting Memoir by A. Ecker, ‘On the Structure and Life of the Contractile Substance of the lowest Animals.’* The contractile substance presented in the Rhizopoda is evidently very nearly allied, physiologically and chemically, as well as in external appearance, to that which Ecker describes in Hydra, and has shown to exist also in other animals, and from the author’s observations on those animals he cannot but confirm Ecker’s statement. This contractile substance, termed by Ecker ‘amorphous’ (an improved edition of Dujardin’s Sarcode), deserves in every case to be further investigated in the way pointed out by Ecker, and to be compared with the contractile elements in the higher animals. Already, as it seems to the author, is an interesting law apparent when all contractile parts are regarded, that only two such occur in the animal kingdom,— Cell-membrane and Cell-contents, which either by themselves alone or together constitute a contractile element. Other parts, such as the cell-nucleus and its derivatives—nucleated fibres, and elastic fibre—amorphous substance not deposited in cells—coagulated fibrine, &c., are never contractile.
1. Contractile cell-membranes occur:
a. In unicellular animals. 1. As universally contractile membranes, such as are met. with in Gregarina, Leucophrys, Coleps, Trachelius, Loxodes, Bursaria, Kolpoda, Uroleptus, and many other infusoria. 2. As motile processes of a contractile or motionless membrane (Opalina, Bursaria, &c.).
b. In aggregated simple cells. 1. As in membranes contractile in toto, as in the heart-cells of the embryo in Alytes and Sepia, the cells of the embryo Planaria, and those in the tail of the larvae in the Tunicata (Ann. d. Sc. Nat. 1846, p. 221), and the caudal vesicle of the Limax embryo (Ecker, 1,c.).
2. As partially contractile membranes, cilia, or epithelium cells.
c. In cells which are united so as to form a tube, capillary lymph, and blood-vessels.*
Contractile cell-contents occur:
a. In unicellular animals. In all infusoria in which there are contractile spaces, a part at least of the contents or parenchyma is contractile.
b. In non-independent cells. The spermatic filaments of animals which are here meant, originate as a deposit in the interior of cells, or, more correctly, in the nucleus of the spermatic cells.
c. In tubes formed out of coalesced cells. Under this bead are to be reckoned the animal or striped muscular fasciculus, in which the contents are represented by the primitive fibrillæ, and the tubes formed out of coalescent cells by the Sarcolemma.*
2. Contractile membranes and contractile cell-contents, united into one body are seen:—
(a) In unicellular animals; premising that Actinophrys and the Rhizopoda come under this head.
(b) In multicellular animals; in which all the cells have coalesced to form a homogeneous substance. Under this head are to be reckoned:—
The Hydrae. These, according to Ecker’s investigations, exhibit no trace of cells—nothing, in fact, but a uniform substance;—they must, therefore, at least according to the author’s view, be regarded as originally composed of a mass of cells, since we know that they are developed from ova, which have undergone the process of segmentation.
The parasite of the venous appendages of the Cephalopoda, which the author has named Dicyema paradoxum, in which exactly the same condition is found to exist as in Hydra (vid. Kölliker’s Bericht üb. d. Zootom. Anst. in Wurzburg, 1849, p. 61).
(c.) Certain cells elongated into fibres in the higher animals —for instance, the so termed muscular fibre-cells or the elements of unstriped muscle; which are to be regarded as elongated cells, in which the membrane and contents are united into a soft substance.
In this enumeration, all those parts of animals which have been distinctly proved to possess a contractile property are contained, and it is consequently apparent that all these parts, taken in a general point of view, fall into but few categories— viz. into two, contractile cell-membranes and motile cellcontents. It is not thence, however, to be inferred that there are but two kinds of contractile elementary tissue, much rather must several such, more or less different, be admitted according as the cell-membrane and its contents assume one form or another.
Such an arrangement as the following appears to be most suitable:—
Contractile elementary tissues are—
1. The amorphous contractile substance = a) a cell-contents; b) one or several cells with membrane and contents united.
2. The spermatic filaments = the formed nuclear contents of a cell.
3. The cilium = an out-growth of a cell-membrane.
4. The contractile vesicle = an entire cell-membrane.
5. The contractile tube = a number of coalescent cellmembranes.
6. The contractile fibre-cell = an elongated cell with membrane and contents united.
7. The contractile fibril-fasciculus (animal muscular fasciculus) = the contents of a series of coalescent cells, which are metamorphosed into a homogeneous contractile tube (vid. Leydig on ‘Piscicola’).
If instead of the anatomical characters, the physiological properties of the contractile parts are regarded, other groupings of them naturally arise; thus, for instance, 1, 2, 3, and in which the movement is wholly independent of nerves, and 5, 6, 7, in which it is effected by nervous influence, would respectively be associated. Besides this, regard must be paid to the relations of the contractile element, to galvanism, cold, mechanical irritation, &c. This is a point, however, which cannot be further’ entered upon in this place, and the author concludes with the expression of a wish that his readers may deduce at least this, from his communication, that what is simple enough in nature affords a key to what is compound, and is therefore worthy of all consideration.
That the Gregarinas are unicellular cannot for a moment be doubted by any one who has once seen these creatures; but, on the other hand, it has hitherto been a question whether they were complete animals or not. The author thinks that this point may now be considered as settled, since his more recent observations (Mittheilung. der Züricher, naturf. Gesellschaft, heft i” 1847, p. 41, and S. and K., Zeitsch., vol. i. p. 1, et seq.), and which have been confirmed by many excellent observations by Stein (Müll. Archiv., 1848, p. 182) have shown clearly that the so-called Pseudo navicellte are the germs of Gregarinse. He would here, however, remark cursorily that the metamorphoses of the Gregarinaä into Pseudo navicellie, apparently from their connexion in pairs, cannot be compared with a conjugation, as Stein is inclined to do, because in this connexion the contents of two Gregarinas are not mixed together as is the case in the conjugation of the alg-v, without exception, with the contents of the united cells.
As there is scarcely any reason for doubting that Euglena properly belongs to the Monadina, and that it is a plant, it should be removed from the above category. Nor has it any distinct cell-wall, being composed wholly of a mass of protoplasm.—T.
S. and K., Ztitsch., B. i. p. 218
That the structureless walls of these canals are of the nature of coalescent cell membrane was shown by the author in the ‘Ann. d. Sc. Nat., 1846.’It is true that Bidder (‘Verhältniss d. Ganglien-Körper zu den Nervenfasern,’ 1847,p. 53) has recently termed the Author’s statements merely conjectures, although, as it would appear, simply upon the ground that they do not accord with his own real conjectures (1. c. p. 54). He adduces no facts contradictory to the Author’s statements, and relies solely upon the law propounded by Reichert, and adopted by no one but himself, and which is altogether incorrect—viz. that elementary forms of different histological importance never enter a continuous connexion with each other.
This is not the place to remark farther upon this question, and the author contents himself with observing, without meaning anything personal, at least this much, that those who upon actual examination of the capillaries of the Batrachian larva do not see that they are formed from outstarting processes and stellate cells, have not claim to the title of microscopist.
Bidder also allows no weight to the Author’s observations on the development of the muscular fasciculus (1. c.,p. 50), relying upon the untenable law of continuity sought to be established by Reichert, and on the observations of Holst and Reichert De Structure Musculorum,’ Dorpat, 1846). The Author, however, maintains his own opinion as the only true one, in opposition to the Dorpat observers. Renewed investigations have shown him that, in the chicken, in the mammalian embryo, and in the Batrachian larva, in all alike, the whole muscular fasciculi originate in series of cells, and that each of the widely separated fibrillar originates in a series of cells, and that they are simply modified cell-contents. This has been recently confirmed also by Bendz, in the Vertebrata, and Leydig, in the Annelida. With respect to the striped muscles, it is not uninteresting to notice the occurrence in them of anastomoses, or branchings of the entire fasciculus. This may be observed in the fasciculi of the auricle of the frog (fig. 6). In this case it will be found that here and there two fasciculi are united by a transverse fasciculus, and that there exists not merely a mutual application of separate fasciculi, but a continuous connexion, an actual coalescence. The Sarcolemma of the three fasciculi in fig. 6, for instance, forms three connected anastomosing tubes, and the primitive fibrillie also pass apparently without any line of demarcation from the one into the other, although it cannot be exactly said that they are actually continuous in the three fasciculi. In the same way Dr. Leydig has noticed very beautiful anastomoses and branchings of the striped muscles in Piscícola (S. and K., Zeitsch., B. i. p. 10S). The author has no doubt but that these anastomosing striped muscles, in part at least, originate in stellate cells; in this case there exists a perfect analogy in the development of the most important higher elementary tissues, inasmuch as that they are all formed, in part by the coalescence of rounded or elongated, and in part by the union, of stellate cells. The latter condition has hitherto been observed in the capillary blood- and lymph-vessels in the terminations of the nerves (S. and K., Zeitsch, B. i., p. 54) and in those of the tracheie in insects.
