20 



GERM- CELL CYCLE IN ANIMALS 



The principal poles are dissimilar ; the end of the egg 

 containing most of the cytoplasm and nearer which 

 lie the nucleus and centrosome is known as the 

 animal pole ; the other end, which is often crowded 



cm* 



Fig. 4. — Germ cells. Ovarian ovum of a cat just before maturity. 

 0.771.= cell membrane; mics. = microsomes; ncl = nucleolus; n. m = 

 nuclear membrane; y/c. aZ. = yolk alveoli. {From Dahlgren and 

 Kepner.) 



with the yolk globules, is called the vegetative pole. 

 The subject of the organization of the egg will be 

 referred to more in detail later (Chapter VIII). 



The male sex cells or spermatozoa differ very 

 strikingly from the eggs. They are usually of the 



