ABSTRACT
The following observations on the development of the spermatozoa in Rana and Helix were made as sequels to a paper published in this Journal “On the Development of the Spermatozoa in the Earth-worm.” The observations have extended over more than a year in each case, and by the kindness of Prof. Laukester I have been allowed to work in the Zoological Laboratory of University College, to whom, for this kindness and for his advice, my best thanks are due.
A. Helix
I was led to make these observations ‘in consequence of finding that in the development of the spermatozoa of Lumbricus a portion of the protoplasm was left behind to serve as a support for the developing spermatozoa. I looked to see if this “blastophoral cell,” perhaps of theoretical interest, occurred in other forms, and taking, by chance, Helix, I found that the spermatozoa were held together at their heads in bundles by darkly granular cells, which, similar in function to the blastophoral corpuscles in the worm, differed from them in the possession of a nucleus (fig. 23).
To determine the relation of this cell to the spermatozoa it was necessary to work through its development, and I continued my observations on Helix, now and then making preparations from other Gasteropoda in which the process seemed to be carried on in a similar way.
If the ovotestis of Helix be opened about the end of summer, in September, and the contents examined, the first and last stages of the series will be seen, the first consisting of spherical cells with relatively large nuclei, in which a well-marked intranuclear network is generally visible; and the last, of mature, or nearly mature, spermatozoa, united by their heads, in most cases, to an irregularly shaped cell, which is noticeable for its dark blue-black granules after treatment with osmic acid.
I say in most cases, because this cell is not present in every bundle, but its absence, I believe, may be accounted for by its having fallen off during the slight teasing necessary to spread the contents of the testis on the slide, or by the fact that the bundles of spermatozoa are cast off, leaving the cell behind.
The mature spermatozoa of Helix exhibit a small pearshaped head, which stains readily with picrocarmine, and a long, slightly flattened tail. Besides the very early stage of the nucleated spermatospore, 1 the first commencement of the formation of the polyplast is evident in cells with two or three nuclei and a corresponding slight segmentation of the enveloping protoplasm. In this state the testis is found during the winter when the animal is torpid, and no further growth takes place till the following spring (Plate XXIV, figs. 1—6).
If the contents of the ovotestis be examined in the spring, in the months of May or June, the spermatospores will be found to have advanced, most of them, to the stage of polyplasts of the ordinary mulberry-like form, consisting of pearshaped spermatoblasts, one of which can be distinguished from the rest by the granular nature of the plasma around it and by the larger size of the nucleus (fig. 9 b, c). This nucleus also, under the action of picrocarmine, takes up a darker hue than that of the surrounding spermatoblasts. It is not so large as the nucleus of the original cell (spermatospore).
This cell is always on the side of the polyplast, next to the wall of the ampulla of the gland, and it is the first appearance of the blastophoral cell, which, from the time of its appearance, undergoes no further division, but remains inactive while the other spermatoblasts continue their process of multiplication more or less supported by it.
During the process of formation of the spermatoblasts the nuclear division appears to take place with no mathematical regularity. The nuclei do not divide at the same time, so that an uneven number of spermatoblasts is as common as an even. In the early stages the cell with three nuclei is as common as that with two or four. It is possible that one of the nuclei of the three-celled form ceases to undergo further change and remains as the blastophoral cell, while the others continue their development; but, as there are no granules or other characteristic marks to distinguish this body before the stage of eight or ten spermatoblasts, it is impossible to say whether this is the case or not.
To see the remainder of the process of the development of the spermatozoa, the contents of a generative gland must be taken about the beginning of August. This appears to consist, as in the earth-worm, in an elongation of the soft viscid protoplasm of the spermatoblast; but the nucleus does not undergo any corresponding increase in length, it is only reduced in size as division proceeds, and finally assumes its mature pyriform shape.
Before any sign of commencing elongation of the plasma is visible, the nucleus appears at the pole of the spermatoblast, next to the blastophoral cell; and soon after this, from the opposite pole, there may be seen a fine whip of protoplasm, which consists of a proximal short, stiffer portion, terminating in a slight knob, and a distal, very fine lashlike part, which requires a good light to make its presence recognisable.
This filament is visible at the extremity of the spermatoblast for some time, but appears to be absent in the mature spermatozoon. It seems as if it served as a guide to the elongating plasma, and became itself swallowed up in the process as it nears completion.
This elongation of the plasma seems to be a kind of flowing down of the semi-viscid substance, for sometimes the greater part of it is found as an irregular or roughly spherical drop collected at the distal end of the spermatoblast; at other times it elongates, as a whole, with various swellings in droplike beads at the distal end, giving it a monilliform appearance.
Division of the nucleus appears to continue after the external plasma has commenced to “drop,” as the mass is not always divided below in correspondence with the nuclear heads; it is not uncommon to find two or three heads connected with a common mass of protoplasm, from the distal end of which there is commonly to be seen a corresponding number of lashes.
As regards the fate of the blastophoral cell after the spermatozoa have left it, I have no observations to offer; but if one may judge by what occurs in other divisions of the animal kingdom, it is extremely probable that it atrophies.
Rana
—Structure of the testis and arrangement of the vasa efferentia.—Though the frog is such a common animal, and its anatomy so perpetually studied, there is not, so far as I am aware, a figure or concise description of the testis and its efferent ducts in this language. I therefore append a diagrammatic woodcut of the right testis (T.) and a portion of the right kidney (k.) with the following description :
Spengel,in his “UrogenitalSystem of Amphibia,” published in ‘Semper’s Arbeiten,’ vol. iii, gives an account of the testis and its ducts as found in Rana, and from this my account is drawn, confirmed by my own observation as far as that has gone.
The testis consists of a series of short tubes, which for want of a better name I have called Crypts (c.), which will be seen in a horizontal or transverse section to be arranged radially around the circumference of the gland. In the centre is an irregular sinus, into which these crypts open, but not in a radial direction ; before doing so, there is a considerable winding and twisting of each crypt (c′). From this sinus, with various communications and branchings which constitute the intratesticular network of Spengel, the vasa efferentia (v. e.) run through the parenchyma of the gland to emerge at the mediad border slightly on the posterior surface. They unite together on the way, and sometimes give off short blind processes. This is the extratesticular network, all the branches of which unite in a canal which is found on the mediad border of the kidney (l. c.). This is Spengel’s “lang canal,” which runs along the mediad posterior, or dorsal surface of the kidney.
When isolated this canal presents a varicose appearance, and from each swelling may be seen a short tube running on the dorsal surface of the kidney towards the ureter, but it soon becomes lost in the substance of the kidney. The time at which to observe these canals and the whole course of the semen is in the spawning time, when by squeezing the gland the vessels become injected with spermatozoa and are conspicuous by their pure white colour.
The urinary tubules into which these canals open, were determined by Spengel to be the collecting tubes or last part which runs transversely across to join the ureter, and so convey the semen to the exterior.
There was no difference discernible in a tube which contained spermatozoa from that which had none.
Development of the Spermatozoa
—The development of the spermatozoa of Rana will be most conveniently described by taking the structure and contents of the testis at four different periods of the year, and from these compiling a complete history of the changes undergone.
If the testis be examined any time from about the end of August or the beginning of September till the spawning time in the spring, it will be found to be full of bundles of spermatozoa arranged radially around the circumference of a testicular crypt (Plate XXV, fig. 1).
If the contents of a testis be received and teased slightly in a drop of salt solution, and then exposed to the vapour of osmic acid and stained, these bundles will be seen to have taken up the staining fluid for the greater part of their length, which represents the nuclear part of the spermatozoon, while at one extremity of the bundle they taper away, generally ending in a slight knot, stained yellow by the picrocarmine, which represents the tail, and is at this stage, when observed fresh, in a state of vibration, like that of the mature spermatozoon. At the other extremity of the bundle is, in the majority of specimens, a mass of a nonstained substance, not granular, or very slightly so, which contains a spherical or ovoidal nucleus, and it was this body which, from its similarity to the blastophoral cell of Lumbricus and Helix, first induced me to follow in detail the history of the development of the spermatozoa (Plate XXV, figs. 2—6).
This body is not found attached to every bundle, but, as the subsequent history will show, it is extremely natural that it should not always be present, as it is left behind when the spermatozoa are shed, and in many cases it would be detached during the slight teasing which is necessary to separate the bundles from each other; the adhesion decreases as age increases.
The bundles of spermatozoa do not lie against the true wall of the testicular crypt; at all times there is to be made out quadrate or roughly spherical cells which represent the testicular epithelium, and more particularly is this the case if the testis be taken about the month of December, when the cells have begun to grow slightly and form a very distinct epithelium between the bundles and crypt wall. (This is shown in fig. 1.) Between these epithelial cells are others of a supporting nature, generally semilunar in shape and darkly stained, which are the interstitial cells. They are particularly well seen when the epithelium is looked down on in a section which has passed longitudinally along a crypt in the right plane, or in sections of the testis of a frog which is not yet sexually mature. Fig. 1 a shows two of these cells from a young testis.
The next stage is to be found in the early summer after the spawning time is over, when the testis is empty of the bundles of the spermatozoa, and consequently rather shrunk in size.
In a teased preparation of this stage are found a few unbroken bundles and many free spermatozoa; but besides these there are peculiar spindle-shaped or irregular cells, which have no definite nucleus, but what seems to be the remains of a broken up nucleus, viz. two, three, or more spherical stained spots, varying in size and in position. Frequently the surface of the cell is marked with striae in the longitudinal direction, and these are due, I believe, to the adhesion of the spermatozoa round this body, representing the blastophoral cell, which as they slide off elongate and mark the cell which supported them (figs. 9—21).
Another very noticeable feature about these cells is the number of vacuoles.
These cells are, I believe, the breaking down blastophoral corpuscles, which, after being drawn out by the sliding off of the bundles, and having served their purpose, are thrown off and undergo degeneration.
In a section of the testis in the lumen of the crypt, intermingled with free spermatozoa and breaking up bundles, are seen the spindle-shaped cells just described, and on the periphery of the crypt the testicular epithelium, as seen in fig.1,spp., where it is beginning to undergo changes of growth; cells are found with several nuclei, often eight, and in many places the epithelium does not consist of a single layer of cells but two, formed by the transverse division of a cell.
In places the degenerated blastophoral corpuscles are seen projecting radially towards the lumen.
The next stage for description is that of the sperm-polyplasts, which is reached about the end of July or the beginning of August. The testis at this stage is considerably swollen and very vascular, showing that growth is rapidly going on. The minute blood-vessels are so full of blood that if the surface be examined under a simple lens the terminations of the crypts are marked out as hexagonal areas by the blood-vessels. In a section (fig. 22) it is seen that the crypts contain large multinuclear masses which almost obliterate the lumen of the tube. They are in various states of progress, the more mature forms projecting as pyriform masses into the crypt, and they are more or less held together by the interstitial cells, so that in making a teased preparation it is exceedingly difficult to free them from one another without breaking them up.
Another important fact about them is that they are hollow vesicles formed of a single layer of cells, and it is towards the centre of the cavity that the spermatoblasts will elongate to form the spermatozoa. The elongation in this case is different to that in Helix, it is centripetal, while that in Helix is centrifugal. At first it seemed a puzzle how from these hollow vesicles the spermatozoa could come to be arranged in bundles, each bundle connected with a nucleus and cell, for at first there was no evidence of a nucleus.
But on examining the sperm-polyplasts in fresh salt solution, and staining with magenta or picrocarmine, keeping the mass under observation while the staining is going on, certain nuclei were seen to take up the staining fluid more rapidly than the rest, two or three to each polyplast, before the others showed more than a faint tinge, while the intermediate mass of plasma swelled up with the water of the solution, and became mapped into areæ corresponding to the spermatoblasts (fig. 23). On more careful examination it was found that these nuclei were superficial to the rest, and were surrounded by a granular protoplasm; and in their general character and colouring seemed to show their connection with the blastophoral nucleus, which is described with the next stage.
In sections stained with haematoxylin an interesting difference of the nuclei of different polyplasts is observed, represented in figs. 27, 28, 29. This appears to be due to changes in the nuclear network, which seems to break up into an irregular mass before the nucleus forms the head of the spermatozoon. The interstitial cells still hold the masses together. About the middle of August the next stage is reached, the hollow vesicle begins to contain developing spermatozoa, which appear to be formed by elongation of the nucleus to form the head and of the protoplasm to form the tail; and when this has progressed some way, so that the head is about half its future length, the vesicle splits and the spermatoblasts fall back, several in connection with one of the superficial nuclei referred to before, on to the wall of the crypt, and assume a radial position. After this the only further change which takes place is the growth in length of the nuclear head till it has attained the size of the mature spermatozoon.
In one section (fig. 31), taken at the right period, a crypt will be found to contain vesicles not yet split, others in the act of splitting (figs. 36, 37, 38), and the spermatozoa arranged more or less radially with reference to a blastophoral cell, and others again which are in the act of being applied to the testicular wall. In this process of sinking back on the parietes of the crypt it seems that the interstitial cells play an important part, from their being connected with the fibres forming the wall as guides to determine the application of the bundle to the wall.
Recapitulation
—The history of spermatogenesis in the frog is then as follows:—Starting with one of the sperinatospores which line the testicular crypts and form the testis epithelium, we find that after spawning is over it commences to grow in preparation for the next year’s stock by division of its nucleus. This process continues until there is formed a hollow body, spherical when freed from the pressure of neighbouring polyplasts, which is the sperm polyplast. The exact mode of the formation of this hollow sphere I am not able to state. Each of the spermatoblasts of this polyplast becomes a spermatozoon, the tail is formed from the plasma by elongation towards the centre of the sphere and the head in a similar or perhaps more complicated fashion. In forming this body all the nuclei are not concerned ; certain of them are left behind, superficial to the rest, and by proper means can be brought distinctly into view. About the end of the summer the spermatoblasts, which are very little different from mature spermatozoa, arrange themselves in bundles round one of these more superficial nuclei, and become with them applied to the wall of the testicular crypt, forming a series of bundles arranged radially round the wall of the crypt, with their tails projecting into the lumen, supported by their heads on the superficial cells, which have now become blastophoral corpuscles.
When the time comes for their being shed the bundles are thrown off and break up, leaving the blastophoral cells behind, which afterwards atrophy by degeneration and breaking up of the nucleus, and are thrown away.
General Considerations and previous Literature relative to Spermatogenesis
—The point on which I wish to lay stress in the previous observations is the existence of a blastophoral cell, which, from the cases I have taken by chance for study, and the figures in the papers of other writers, seems to be of very general distribution. The question naturally arises, What is its morphological significance ?
When I found the body in the earth worm Professor Lankester told me of a suggestion which had been made to him by Professor Van Beneden, of Liège, viz. that it corresponded to the ovum whilst the spermatoblasts correspond to the polar vesicles or directive corpuscles which are thrown off from the ovum previous to fertilization. These bodies, of very general occurrence, are hard to explain. Balfour (this Journal, vol. xviii, p. 123) says, “I would suggest that in the formation of these polar cells, part of the constituents of the germinal vesicle which are requisite for its functions as a complete and independent nucleus, are removed to make room for the supply of the necessary parts to it again by the spermatic nucleus,” and it may be that as the polar cells represent the elimination of a male element from a cell whose future destiny is female, so the formation of the blastophoral cell represents the same ridding of the female element from a cell whose destiny is male.
After the publication of a paper “On the Development of the Spermatozoa of Lumbricus “(this Journal, April, 1880), I received a paper from Mr. Minot, published in the ‘American Naturalist ‘for February, 1880, in which, from theoretical considerations, he arrived at the conclusion that some such structure as the body alluded to above must be found in the development of the spermatozoa, and records Semper’s “Observations on the Development of Spermatozoa in Elasmobranchs “in support of his view, in which Semper describes a part of the original cell which is left behind as “Mutterkern,” though it is evidently the same as our blastophoral cell.
The considerations offered above are, of course, pure speculations, and it is quite possible that these blastophoral cells have no morphological significance, but function as bodies for the support and nutrition of the young spermatozoa, and, having performed this duty, undergo degeneration and disappear.
We have seen that, in Rana, from one original cell more than one blastophoral cell is developed, and this seems to be paralleled by what takes place in Insects, as fig. 25, Plate XXIV, from Dytiscus, and figs. 26 and 27 from Pieris, will show. The exact origin of these cells in Insects I have not determined, but at the first glance they seem comparable to a large extent to the “superficial nuclei” of Rana.
The literature on the development of the spermatozoa is very copious, more particularly that which treats of the development in Mammals, as may be seen by reference to the papers of von la Valette St. George in the ‘Archiv fiir Mikr. Anatomie.’
I do not propose to consider every individual publication, but to mention those who have put forward plans of spermatogenesis capable of application to the whole, or at any rate large, divisions of the animal kingdom; but before doing this I may briefly state what my own views on the subject are.
A cell whose future destiny is male (spermatospore) commences to undergo changes which fit it for its new function, and by a process of multiplication gives rise to many fertilising elements. The first steps are division and multiplication of the nucleus, and a corresponding constriction of the surrounding plasma, till a multicellular mulberry-like mass (sperm-polyplast) is produced, which may be solid or hollow, consisting of young spermatozoa or spermatoblasts. During this process some portion or portions of the original cell cease to undergo further change and remain behind to support and nourish the developing spermatozoa (blastophoral cell).
The nucleus of the spermatoblast forms the head of the spermatozoon, and the tail is formed by the centripetal or centrifugal elongation of the plasma. When fully formed the spermatozoa are supported on the blastophoral cells till required and then shed off, leaving their supports to atrophy and decay.
How far this view holds good for the Mammalia I am not able to say precisely, but the abundance of figures confirming the above account in papers treating on this subject, justifies the idea (compare the account below of Meyer’s paper) that spermatogenesis will be found to be essentially the same in that class.
Many of the figures show the blastophoral cell under various names, and represent stages which seem in most respects comparable to those found in the spermatogenesis of Helix.
Kölliker (‘Zeit, für Wissen. Zool.,’ Bd. vii, p. 201) seems to have been the first to give a plan of spermatogenesis. He gives figures of developmental stages from the bull, pigeon, frog, and carp; at the same time noting that the account holds good for all animals.
He believed that the spermatozoa were developed by a direct metamorphosis of the nuclei of the cells of the testis. This change takes place in what he calls “Bläschen,” which are probably nothing more, as Meyer suggests, than polyplasts modified by the fluid (Müller’s) with which he treated them. He conceived that the tail as well as the body originated from the nucleus.
He very shortly describes the process in the frog, but with the exception of the figures, which show well the bundles of spermatozoa united by the blastophoral cells, there is little agreement between my account and his.
V. la Valette St. George has, in his fifth communication, “On the Development of the Spermatozoa,” to Max Schultze’s ‘Archiv,’ Bd. xv, p. 261, given an account of spermatogenesis in general.
The paper commences with an exhaustive resume of previous observations and papers published in connection with the subject, and then gives an account of the process as he has observed it in many Mammalia—bull, ram, stallion, rabbit, &c., and ends with a summary which embodies his ideas of spermatogenesis based on his former papers. He recognises in the testis tubule two kinds of cells. Of the first, he says, “Peculiarly like young ovarian cells they are destined to multiply as Ursamenzellen or Spermatogonia; in a similar manner by division and by transformation of their descendants (the Spermatocytes) they are destined to give rise to the spermatosomes (Samenkörperchen). They produce a mass of cells which either by an arrangement of the peripheral cells develop a special cover—Keimkugeln, Samenkugeln, Spermatocysten (Insects and Amphibia), or remains coverless—Samenknospen, Samensprossen, Sperma-togemmse, whilst the protoplasm which belongs to each cell is more or less segmented. In many cases one of the cells resulting from the division or its nucleus is preserved at the foot of the Spermatogemmæ.”
“The second kind of cell which I call follicle cells are bound together into a tissue which, while it embeds the Spermatogonia, also covers and protects the Speratomgemmae in their multiplication by division.”
From this it will be seen that he recognises the cell which is formed at the base of the Spermatogemmae as being part of the original cell which has been left behind in the growth and multiplication of the others, but he does not appear to recognise the similarity between this cell and those which are found in the Spermatogemmae or Samenkugeln of the frog which is formed in the same way, and has a similar function.
In Semper’s “Monograph on the Urogenital System in Elasmobranchs” (‘Semper’s Arbeiten,’ Bd. ii), he gives an account of the development of the spermatozoa. The section of a mature ampulla, with its bundles of spermatozoa, is very like that of the frog; each bundle is connected with a nucleated mass which rests on the wall of the ampulla, and which he calls, from its protective function, “Deckzelle,” though he recognises it as being the remains of the Mutterzelle. He traces the fate of these bodies after the spermatozoa are shed, and finds that they undergo fatty degeneration, the nuclei fall together and are only held together by a granular detritus, while the ampulla itself collapses. This he compares to the formation of the corpus luteum in the ovary. In Elasmobranchs there is a continuous development of spermatozoa in the testis from within out, so that we get degenerated ampullae, full ampullae, ampullae with spermatozoa developing, and the formation of ampullae in the same testis, not coming as in Rana in successive crops from the same ampulla. The spermatozoa do not develop as in Rana from vesicles (hollow polyplasts), but on a plan more like that of the snail. He calls the young immature spermatozoa spermatoblasts, and says that he was unable to make out the origin of the tail.
Klein, in his ‘Atlas of Histology,’ gives an account of spermatogenesis based on researches on man, rabbit, mouse, &c. In the contents of the seminal tubules he recognises two kinds of cells, the inner and outer seminal cells. The latter present two kinds according to the state of the nucleus; in one kind the nucleus is finely granular, in the other it is devoid of a limiting membrane, and has rods or filaments twisted in many directions in its interior. Nearer the lumen of the tubule are the inner seminal cells, which are seldom limited to one or two layers. They do not directly touch each other, but are joined by an interstitial substance. These cells are polyhedral from mutual compression, and their nuclei are similar to the second type of the outer seminal cells, that is, they contain rods or filaments variously arranged. Their nuclear rods vary in shape and arrangement, which he considers indicative of division and multiplication. Nearer still to the lumen of the tube the cells are loosely connected, and they may be seen dividing each into two daughter nuclei. These small cells, the daughter cells, undergo changes leading to the formation of the spermatozoa, and for these he uses Sertoli’s term spermatoblasts. The first change is seen in the nucleus, which becomes finely granular and assumes a membrane. This kind of nucleus he calls the resting nucleus. At the same time it moves to one pole of the cell, which is itself elongated, and constitutes a “granular mass,” separated from the nucleus by a “clear bag.” When the young spermatozoa are in this state they assume a definite arrangement, and become placed in fan-shaped groups along the tubule, with the handle of the fan sunk among the seminal cells; their further progress consists in elongation. He then goes on to mention the views of Ebner and Neumann, who consider that the groups of spermatozoa are formed in a single cell which consists of a base, which has (Ebner) or has not (Neumann) a nucleus next the membrana propria, a peduncle, and a broad mass at the end of the peduncle in which the spermatozoa are produced.
He regards the head, as well as the “middle piece,” as formed from the nucleus.
In Rollett’s ‘Untersuchungen aus dem Institut für Phys, und Hist.’ for 1871, there is a paper by v. Ebner, in which he gives an account of the development of the spermatozoa in the rat and mouse, referring to other mammals, and a series of drawings illustrating that process in the first-named animal.
He divides the processes into eight stages, which I will not enumerate, but try to epitomize his account. The fundamental idea in which he differs from other writers is in the existence of a “Keimnetz,” in which the spermatozoa are developed. This consists of a welded mass of cells next the tunica propria of the tubule in which two kinds of nuclei are discerned, the one pale, nucleolated, with distinct outline; the other granular, dark, with an indistinct outline. On taking a superficial view of this layer it has the appearance of a network. From it processes project towards the lumen of the tubule which, when first formed, are nothing but plasma; then nuclear hardenings commence at its inner extremity, which soon unmistakably assume the appearance of spermatozoa heads, in this case being pointed at one end, which end is directed towards the periphery. The tails are formed from the plasma. At the base of this process, which he calls a spermatoblast, there is often a nucleus, which can be distinguished by its slightly irregular shape, and from its being elongated in the direction of the spermatoblast, but he gives no account of the origin or fate of this nucleus.
The spaces between the processes of the “Keimnetz “are filled up with cells of various sizes and in various states of multiplication. These he regards not as in any way concerned with the formation of the spermatozoa, but only present to assist the growth by supply of nutritive material to the young spermatozoa; and he traces their origin to their having wandered from the lymph spaces of the testis. As regards their fate, he believes that they form the coagulated particles, or “Eiweisskugeln,” which are to be found in the lumen of the tubule of a ripe testis. Sometimes these bodies contain crumpled-up semilunar nuclei.
It is obvious from this that part of the “Keimnetz “corresponds to my testicular epithelium, the outer seminal cells of Klein, and the “Ursamenzellen “of other writers; moreover, the two kinds of cells which Klein mentions as being in an active or passive condition, according to the condition of the nucleus, are here clearly indicated.
As regards his spermatoblast, he says that, as far as his observations went, it arose without any division of a nucleus, but in this I believe he will be found to be mistaken. And it is my opinion that the nucleus at the base, and the nuclei, as he says, newly, formed at the other end, are due to a division of one cell.
As regards the cells which lie in the meshes of the network, and which, he thinks, are only of use for the nourishment of the spermatozoa, the opinion of almost every other writer is that they are concerned in the formation of the spermatozoa and represent various stages of the process. These are the inner seminal cells of Klein, the Spermatogemme and Samenknospen of v. la Valette St. George, and the idea that they form the “Eiweisskugeln,” and similar bodies found in the lumina of the tubules, is untenable.
I think these bodies will be found to owe their origin to the breaking up of blastophoral cells which, as in the frog, after the spermatozoa are ripe and have dropped from their supports, themselves are thrown off and undergo fatty degeneration.
It may be mentioned that he considers the middle piece to arise from the same consolidation of plasma as the nucleus.
In the ‘Archiv fur Mikr. Anatomie,’ vol. xviii, p. 233, Prof. Flemming has a paper in continuation of his researches on cells and nuclei, in which he gives an account of the formation of the spermatozoa in salamander. The interesting point for our purposes is that which refers to the formation of the head of the spermatozoon, not, as has been supposed since the observations subsequent to Kolliker’s paper appeared, from the whole nucleus, but from that part of it which he calls the “chromatin.” This collects into a spirally folded mass, which becomes more closely folded as it increases in length, till the whole head may be seen coiled up in the nucleus. The origin of the tail he traces to the cell plasma. These observations agree with those of Kôlliker if we substitute spermatozoon head for the whole spermatozoon.”
I have not worked with sufficient detail, to determine the exact origin of the spermatozoon head, but I must confess that my ideas agreed with those of previous observers that the whole nucleus took part in the formation of this structure, though, since the publication of Flemming’s paper, I should not like to say that it was so, and can only hope to make some observations on its exact origin in the Mammalia. In the earth-worm it is not possible to distinguish in the nucleus “chromatin” from other constituents, and hence the head of the spermatozoon cannot be traced in this case to such an element..
The most recent utterance on this subject is by Meyer, in the ‘Memoirs of the St. Petersbutg Academy,’ tome xxxii, 1880, and as it contains many figures confirmatory of my views, I purpose to give a slightly more lengthy account of it.
His observations were made on the dog, cat, rat, mouse, bear, rabbit, and guinea pig. In a testicular tubule next the wall are found the Ursamenzellen, which consist of two kinds of cells, one small, often darkly granular, which he calls follicle cells, the other larger, with large nucleus, each containing a nucleolus, the nucleus itself being surrounded by a clear plasma.
These would be the outer seminal cells of Klein, or what I have called the testicular epithelium and its interstitial cells.
The first change which an Ursamenzelle undergoes is division. This takes place in a tangential direction, and the cell which is directed towards the lumen of the tube takes on the characters of a spermatocyte, which consists in the nucleus and plasma becoming darker and more granular (cf. his Taf. ii, fig. 94). The spermatocytes thus formed by division from the Ursamenzellen gradually increase in size and assume an oval form. The next stage consists in a multiplication of this nucleus, apparently by its breaking up and a reappearance of the pieces in two or three places, producing a corresponding number of nuclei. By a repetition of this process the Spermatogemme is produced (figs. 9—29, Taf. i). These bodies he regards as fundamentally a collection of several cells, and in support of this view adduces the fact that a single spermatocyte may run its course to a mature spermatozoon without presenting this form, never possessing more than one nucleus. These bodies have a radial arrangement in the testicular tubule and an elongated shape from the pressure of the surrounding cells, but they are generally spherical when isolated and floating free in a liquid.
The last stage is the change of the nucleus to form the head and the division of the plasma of the Spermatogemme into tongue-like processes which form the tail. The first change varies according to the animal examined, that is, to the shape of the spermatozoon head. He regards the middle piece as derived not from the nucleus, but from the plasma. The rest of the plasma which has taken no part in the formation of the spermatozoa remains behind for a time to support them, but finally undergoes a kind of fatty degeneration.
He recognises the existence of v. Ebner’s spermatoblasts under the name of “Samenähren,” and says that “intermediate forms may be seen from the spermatocyte to the mature ‘Samenähren’ connected with the Ursamenzelle, to which they owe their origin, by a process of plasma (figs. 35, 36, 38, 40).’’
He disagrees with v. la Valette St. George in thinking that the interstitial cells do not multiply at the same time as the Ursamenzellen, and form layers round the spermatocytes and Samensprossen as the last named observer does.
From this account it will appear that his Samenähren are the bases of v. Ebner’s spermatoblasts, and correspond to the cell which is left at the foot of the Spermatogemme described by v. la Valette St. George.
The foregoing papers of which I have given an account are few out of many, but they embody the results of those which I have not mentioned, and taking into consideration the facts and drawings given in them it seems possible to reconcile to a large extent the different accounts of spermatogenesis in mammals in the following short résumé, omitting as far as possible the particular terms used by each author. The wall of the testis is lined on the inside with a testicular epithelium, in which the true testis cells are supported by interstitial cells. One of these testis cells divides tangentially, giving rise to two cells which are held together by a common plasma; the cell next the lumen of the tube grows and the nucleus multiplies, giving rise to several (8— 12, according to v. Ebner) nuclei embedded in a plasma; or, according to Meyer, the cell and its nucleus may proceed to form a single spermatozoon without multiplication. These nuclei form the heads of the spermatozoa, and the plasma the tails. When nearly mature the young spermatozoa are supported on the plasma, but when they are ripe they are cast off from it and enter the lumen of the tube. After the spermatozoa have left it this body itself is thrown off with its nucleus, which has remained at its base, and undergoes fatty degeneration, being found in the lumen of the tube in this state.
For convenience I append a list of synonyms which are used by various authors in describing the process of spermatogenesis.
1. Spermatospore = Spermatogone (St. George, Meyer).
1a. Spermatocyte, intermediate form (St. George).
2. Sperm-polyblast — Blaschen (Kolliker), consisting of the following :
3. Spermatoblasts = Spermatoblasts of Semper, Klein, Sertoli, or Samen sprossen or Spermatogemme (St. George, Meyer).
4. Mature spermatozoa, united into bundles by blastophoral cells (sperma toblasts, v. Ebner). Samenahren (Meyer).
5. Spermblastophor = Deckzellen of Semper.
6. Testicular epithelium = Ursamenzellen (St. George).
7. Interstitial cells = Follikelzellen (St. George, Meyer).
With reference to these and other terms, see my former paper, this Journal, January, 1880, and also the list of terms at the end of the present paper.