484 



SEMEN. 



enclosed by a lesser or greater number of but here, as well as in the Lacerta, &c., the 

 cyst-like mother cells (fig. 350.). The size of formation of the spermatozoa only takes place 

 each of these cysts amounts to about i^'", 



wherever the number of the enclosed cells Fig. 353. 



is small ; but in the reverse case it may in- 

 crease to a 1 /". The cells of developement 

 dissolve after the formation of the sperma- 

 tozoa, and the latter then get into the in- 

 terior of the cyst (fig. 351.). "The spiral wind- 



Fig.351. 



Spermatozoa in the interior of the cysts (Toipedo 

 Narce). 



ings of the body seem to be still wanting 

 at this stage, or, at least, not to be perfectly 

 developed. If the number of spermatozoa is 

 only small in one cyst, they never group 

 together into a bundle, whilst this is con- 

 stantly occurring in the reverse case (fig- 352.). 



Fig. 352. 



Bundle of Spermatozoa in a cyst (Torpedo Narce). 



We will not venture to decide, however, whe- 

 ther this difference is entirely attributable to 

 the greater number of the cells of develope- 

 ment ; and we are the less inclined to do so, 

 as we have already seen, when investigating 

 the spermatozoa of birds, that, even with an 

 equal number of the formations alluded to, 

 the grouping of the spermatozoa in the in- 

 terior of the cyst may be different. This 

 much, however, is certain, that the num- 

 ber of the enclosed cells is not entirely with- 

 out influence. The fact of the fascicles of 

 spermatozoa always coinciding in one cyst 

 with a greater number of the cells of develope- 

 ment, seems, at all events, to favour this con- 

 jecture. 



Previous to the period of procreation, we 

 also find, in the testicles of the osseous fishes, 

 that the cells of developement are enclosed 

 in the interior of larger cells (j%. 353.); 



Spermatic cells from Cyprinus brama. 



subsequently to the destruction of the cyst, 

 and to the consequent independence of the 

 cells of developement. We infer this from the 

 circumstance that we have never seen in them 

 any real bundles of spermatozoa. The state- 

 ment of Kolliker that the spermatozoa of Am- 

 phioxus develope themselves from little cells 

 (of ToW'-Tic/"), which lie together in 

 groups of from six to twenty-five, also seems 

 to support the correctness of our conjecture. 

 Each of such groups appears to us to be the 

 brood of a single mother cell. The mother cells 

 themselves, however, are of such a small size, 

 that the formation of such brood in their inte- 

 rior is not to be traced or perceived. It can 

 only be seen that these cells gradually lose 

 their round shape, and that they assume a pear, 

 or spindle-like form. This, unquestionably, is 

 merely the consequence of the endogenous 

 developement of a spermatozoon, which gra- 

 dually stretches itself, thereby causing (as in 

 Gallus, Rana, &c.) the change of shape of the 

 external enclosure. 



Thus much of the proportions of form, and 

 of the mode of developement of the sperma- 

 tozoa among the Vertebrata. We have treated 

 this subject somewhat elaborately, partly be- 

 cause the spermatozoa of these animals are 

 those which may be most frequently obtained 

 for observation, partly also because it is in 

 them that the stages of developement can be 

 better traced and recognised. We have invariably 

 met with in them a common type, not merely 

 in the external shape, but also in the mode of 

 developement of the spermatozoa ; and these 

 are circumstances which will be of importance 

 to us in interpreting the stages of developement 

 of the spermatozoa in the lower animals, in 

 which they are as yet enveloped in great ob- 

 scurity. 



MOLLUSCA. Among the Invertebrata, the 

 division of the Mollusca uniformly possesses 

 (as in the Vertebrata) filiform spermatozoa, 

 which are enlarged at the anterior extremity. 

 This anterior extremity does not, however, 

 every where form a particular division, as a 

 body, distinct from the posterior thinner part or 

 tail. On the contrary, the one passes in many 

 cases so gradually into the other, that it is im- 

 possible to determine the boundary between 

 the two. The tail then appears to be a mere 

 pointed continuation of the anterior enlarged 

 part. The two thus distinct forms of sper- 

 matozoa are, however, again united with one 

 another in various ways. 



