GROWTH AND DIFFERENriAriON OF THE GERM-CELLS II5 



cells of the Qg^ 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 bv the fact that such a sacrifice occurs in some animals after 

 the eggs have been laid. Thus in the earthworm, Liiuibricus tcrrcs- 

 ti'is, 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.^ 





Fig. 58. — Ovarian eggs of insects. [KoRSCHELT.] 



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

 branching nuclei; g'.v. germinal vesicle. B. Egg of water-beetle, /?)'/«««, living; ihe egg {o.v.) 

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

 dark mass of food-granules. 



{b) Differentiation of the Cytoplasm and Deposit of Dcutoplasni. — 

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

 from deutoplasm. As the ^^^ 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. 



