62 



COMPARATIVE PHYSIOLOGY. 



with nucleated epithelial cells, from which, by a series of 

 changes figured above, a. general idea of their development may 

 be obtained. 



It wiU be observed that throughout the series the nucleus of 

 the cell is in every case preserved, and finally becomes the head 



Pig. 61.— Spermatogenesis. A— H, isolated sperm-cells of the rat, showing the devel- 

 opment of the spermatozoon and the gradual transformation of the nucleus into 

 the spermatozoon head. In G the seminal granule is being cast off (after H. H. 

 Brown). I— M, sperm-cells of an Elasmobranch. The nucleus of each cell divides 

 into a large number of daughter-nuclei, each one of which is converted into the 

 rod-like head of a spermatozoon. N, transverse section of a ripe cell, showing 

 the bundle of spermatozoa and the passive nucleus (I — N, after Semper). O^S, 

 spermatogenesis in the earth-worm; O, young sperm-cell; P, the same divided 

 into four; Q, spermatosphere with the central sperm-blastophore; R, a later stage; 

 S, nearly mature spermatozoa. (After Blomfleld.) 



