REPRODUCTION 



37 



material of the nucleus. The "ripe" sperm cell is essentially a motile 

 nucleus. 



Fig. 27. — Cross sections of testis tubules of a mouse. BV, blood vessel; F, fat 

 granules; IC, interstitial cells; S'-, spermatogonia; S^, spermatocytes; 5^, spermatids; 

 SP, spermatozoa; ST, sustentacttlar cells. X360. (Redrawn from Bremer, Text-book 

 of Histology.) 



VESICULAR FOLLICLE^ 

 OVUMn 



(OVUM 



/PRIMARY FOLLICLE 



LLicuLAR'"'^^%J"^-v---;ii;^4^^i^^i'^^ 



LLs ^ ^ ^'>••fiH^^r^^■■'■■ 



/ 



FOLL 

 CELLS 



Fig. 28. — Section through cortical region of the ovary of a mouse showing young 

 (primary) ovarian follicles and older (vesicular) follicles. X76. 



The egg, in contrast to the spermatozoon, not only retains its original 

 cytoplasmic volume but, while still in the ovary, passes through a long 



