u6 



THE GERM-CELLS 



of the cytoplasm and the formation of the yolk. Both its origin and 

 its physiological rdle are, however, still involved in doubt. 



The deutoplasm first appears, while the eggs are still very small, 

 in the form of granules which seem to have at first no constant posi- 

 tion with reference to the egg-nucleus, even in the same species. 



Fig. 59. Young ovarian eggs, showing yolk-nuclei and deposit of deutoplasm. 



A. Myriapod (Geophilus) with single " yolk-nucleus " (perhaps an attraction-sphere) and scat- 

 tered deutoplasm. [BALBlANl.] 



B. The same, with several yolk-nuclei, and attraction-sphere, s. [BALBlANl.] 



C. Fish (Scorp&tta), with deutoplasm forming a ring about the nucleus, and an irregular mass 

 of "eliminated chromatin" (? yolk-nucleus). [VAN BAMBEKE.] 



D. Ovarian egg of young duck (3 months) surrounded by a follicle, and containing a " yolk- 

 nucleus," y.n. [MERTENS.] 



Thus Jordan ('93) states that in the newt (Diemyctylus) the yolk may 

 be first formed at one side of the egg and afterwards spread to other 

 parts, or it may appear in more or less irregular separate patches 

 which finally form an irregular ring about the nucleus, which at this 

 period has an approximately central position. In some amphibia 

 the deutoplasm appears near the periphery and advances inwards 



