68 SURVEY OF THE REPRODUCTIVE PROCESS 



III. 



SURVEY OF THE REPRODUCTIVE PROCESS IN 

 THE ANIMAL KINGDOM. 



1. THE function of reproduction in the Animal Kingdom, 

 while it embraces wide variations in accessory points, pre- 

 sents a great, if not an absolute, uniformity in the produc- 

 tion and conformation of the sexual elements. The sper- 

 matic particles, or spermatozoa, are developed as the solitary 

 nuclei of secondary cells the vesicles of evolution which 

 are in turn generated in variable numbers within the cells 

 occupying the cavities of the spermatic gland. When 

 liberated by the rupture of their envelopes, the particles 

 float freely in the fluid secreted by the gland singly or in 

 bundles as the case may be. Their normal form is that of 

 a minute rounded body, with a long filiform appendage or 

 cilium, by the vibration of which an onward motion is given 

 to the whole corpuscule. Both parts are sufficiently ap- 

 parent in the higher animals, but among the lower tribes, 

 as, for instance, in insects, we find the body sometimes so 

 much attenuated as to be undistinguishable from the 

 cilium, while in other cases the latter appendage disappears, 

 and with it the motile power. This modification obtains 

 in some Crustacea and Entozoa.* 



The germinal corpuscula, on the other hand, appears in 

 the form of a minute nucleated body, and is known as 

 the germinal vesicle. Like the spermatozoon it seems to 

 be developed as the nucleus of a secondary cell (the ovum), 

 which is generated in the interior of another (the ovisac), 



* Siebold's Compar. Anat., 3-18, 290, 117. 



