GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 157 



most, if not in all, cases breaks up into smaller and smaller fra^^ments 

 which contribute, directly or indirectly, to the cytoplasmic f^rowth. 

 In all these cases the history of the yolk-nucleus is such as to indi- 

 cate the participation of the nucleus in its formation. Calkins (95) 

 endeavours to show that the yolk-nucleus in Luvibricus is directly 

 derived from the nucleus by a casting out of a portion of the chro- 



r^\ 



r. 



p 



o 



^^ 



H 



Fig. 80.— Yo'k-niicleus in earthworm, spider, and ascidian. [././?, Cai.KINS ; C-E, Va.n 

 Bambeke; F-L Cka.mpton.] 



A. Early ovarian egg of Z,?Yr;«(5r/V//^. B. Later stage; fragmentation of yolk-nucleus. C. Ova- 

 rian ^gg of PholcHS. D. Later stage; disintegration of yolk-nucleus. E. Remains of the yolk- 

 nucleus scattered through the cytoplasm. F. Early stage of yolk-nucleus in Mo/^^uhi. G-I. Dis- 

 integration of the yolk-nucleus and enlargement of the products to form deutoplasm-spheres. 



matin-reticulum — a result agreeing in principle with earlier obser- 

 vations on other eggs by Balbiani, Henneguy, Leydig, Will, and 

 other observers. This conclusion rests partly on the apparent direct 

 continuity of yolk-nucleus and chromatin, partly on the staining- 

 reactions. Thus when treated with the Biondi-Khrlich mixture (basic 

 methyl-green, acid red fuchsin), the yolk-nucleus at first stains green 

 like the chromatin, while the cytoplasm is red, and this is the case 



