154 



THE GERM-CELLS 



egg cannot be explained as the result of a simple mechanical dis- 

 placement of the germinal \esicle by the yolk, as some authors have 

 maintained. 



The primary origin of the deutoplasm-grains is a question that 

 involves the whole theor\' of cell-action and the relation of nucleus 



Fig. 78. — Young ovarian eggs, showing yolk-nuclei and deposit of deutoplasm. 



A. Myriapod {Gcop/nlus) with single "yolk-nucleus" (perhaps an attraction-sphere) and scat- 

 tered deutoplasm. [Balbiani.] 



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



C. Fish {Sco?-p(Ei!a), with deutoplasm forming a ring about the nucleus, and an irregular mass 

 of " eliminated chromatin" (? yolk-nucleus). [\'aN' Bambekf,.] 



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

 nucleus," >'.«. [Mertens.] 



and cytoplasm in metabolism. The evidence seems perfectly clear 

 that in many cases the deutoplasm arises /// sit?i in the cytoplasm 

 like the zymogen-granules in gland-cells. But there is now also a 

 very considerable body of evidence indicating that a part of the 

 egg-cytoplasm is directly or indirectly derived from the nucleus 

 through the agency of the yolk-nucleus or otherwise ; and the 



