GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 



157 



most, if not in all, cases breaks up into smaller and smaller fragments 

 which contribute, directly or indirectly, to the cytoplasmic growth. 

 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 Lumbricus is directly 

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



Fig. 80. Yolk-nucleus in earthworm, spider, and ascidian. [A, B, CALKINS; C-E, VAN 

 BAMBEKE; F-I, C HAMPTON.] 



A. Early ovarian egg of Lumbricus. B. Later stage; fragmentation of yolk-nucleus. C. Ova- 

 rian egg of Pholcus. D. Later stage; disintegration of yolk-nucleus. E. Remains of the yolk- 

 nucleus scattered through the 'cytoplasm. F. Early stage of yolk-nucleus in Molgula. 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-Ehrlich 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 



