202 GERM-CELL CYCLE IN ANIMALS 



gonia of the second order (Fig. 5$, E). Those in- 

 different germ cells that are to form oocytes grow 

 large, remain in the germinal epithelium, and do not 

 divide. They possess a double nucleolus (Fig. 58, F). 

 When a diameter of 36 microns is attained, the 

 oocyte passes out of the hermaphroditic gland into 

 the uterus. 



The nurse cells, like the oocytes, remain in the wall 

 and do not divide ; their nuclei grow to be about 15 

 microns in diameter and the chromatin forms irregu- 

 lar clumps more or less evenly distributed (Fig. 48, B) . 

 No differences could be discovered in the indifferent 

 germ cells by means of which the future history of 

 these cells could be determined. It was noted, how- 

 ever, that egg cells were never present without a 

 neighboring nurse cell, and the conclusion was 

 reached that a favorable position with regard to a 

 nurse cell determines whether an indifferent germ 

 cell shall develop into a spermatogonium or an egg. 

 If Buresch's observations are correct, Helix is not 

 protandric, but both sorts of germ cells mature at 

 the same time, and the fate of an indifferent germ 

 cell depends upon nutrition, that is, its proximity 

 to a nurse cell. 



Demoll (1912&) has proposed a new hypothesis 

 regarding sex determination and has selected certain 

 events in the oogenesis and spermatogenesis of Helix 

 pomatia as arguments in its favor. The hypothesis 

 is that the accessory chromosome (see Chapter IX) 

 contains the anlagen of the male sexual characters, 

 whereas the female sexual characters are localized 



