176 



GERM-CELL CYCLE IN ANIMALS 



Meyer (1895) extended the study of chromatin- 

 diminution to other species of Ascaris. In A. lum- 

 bricoides no diminution takes place until the four- 

 cell stage ; then three of the nuclei become deprived 

 of part of their chromatin. A diminution of this 



PI O Q O O O O 



n o o o o o o 



o o 



Fig. 52. — Ascaris. Diagram showing segregation of primordial germ 

 cell. E = egg ; Pi, P2, P3 = stem cells ; P4 = primordial germ cell. 

 Circles represent somatic cells. (From Boveri, 1910.) 



sort had been described by Boveri as a variation in 

 the process observed in A. megalocephala. In A. 

 rubicunda the differentiation of the cleavage cells 

 seems to resemble A. megalocephala more than it 

 does A. lumbricoides. Only late cleavage stages 

 of A, labiata were obtained by Meyer, but there is 



