GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 115 



cells of the egg which have sacrificed their own development for the 

 sake of their companions, or whether they have had a distinct origin 

 from a very early period. That the former alternative is possible is 

 shown by .the fact that such a sacrifice occurs in some animals after 

 the eggs riave been laid. Thus in the earthworm, Lnmbricus terres- 

 tris, several eggs are laid, but only one develops into an embryo, and 

 the latter devours the undeveloped eggs. A similar process occurs 

 in the marine gasteropods, where the eggs thus sacrificed may 

 undergo certain stages of development before their dissolution. 1 



Fig. 58. Ovarian eggs of insects. [KORSCHELT.] 



A. Egg of the butterfly, Vangssa, surrounded by its follicle; above, three nurse-cells (n.c.) with 

 branching nuclei; g.v. germinal vesicle. B. Egg of water-beetle, Dytisciis, living; the egg (o.v.) 

 lies between two groups of nutritive cells ; the germinal vesicle sends amoeboid processes into the 

 dark mass of food-granules. 



(b) Differentiation of tJie Cytoplasm and Deposit of Deutoplasm. 

 In the very young ovum the cytoplasm is small in amount and free 

 from deutoplasm. As the egg enlarges, the cytoplasm increases 

 enormously, a process which involves both the growth of the pro- 

 toplasm and the formation of passive deutoplasm-bodies suspended 

 in the protoplasmic network. During the growth-period a peculiar 

 body known as the yolk-nucleus appears in the cytoplasm of many 

 ova, and this is probably concerned in some manner with the growth 



1 See McMurrich, '86. 



