476 STANLEY C. BALL 



Of investigators who considered the yolk-nucleus to be de- 

 rived from the nucleus Calkins mentioned Shafer ('83) who ob- 

 served m the fowl's egg that the yolk-nucleus was connected 

 with the germinal vesicle by numerous fine striations; Balbiani 

 ('83) who claimed that in the Geophiljdae it originates by direct 

 transformation of the parts of the nucleolus of the germinal 

 vesicle. Leydig ('88) saw the nucleolus in Triton become 

 amoeboid and wander out into the cytoplasm where it finally 

 broke up into granules around the periphery of the yolk. Finally 

 he cites Henneguy ('93) and Balbiani ('93 )who both found 

 that in various eggs the yolk-nucleus originates from the 

 nucleolus. 



As a result of Calkins' own observations ('95) on the eggs of 

 Lumbricus he concluded that the yolk-nucleus is of nuclear 

 origin. He found it lying on the margin of the nucleus in direct 

 connection at several points with the chromatin; the nucleolus 

 takes no part in its formation. After migrating into the cyto- 

 plasm he conceived the granules of which it is composed as sepa- 

 rating and forming the yolk plates after undergoing a change in 

 chemical composition. 



Wilson ('96), in "The Cell in Development and Heredity" 

 speaks broadly of the yolk-nucleus, conveying the impression 

 that already the body was beginning to be looked upon as not 

 having, perhaps, so much importance as a functional cell organ 

 as had previously been attributed to it. He says in part: 



Calkins' observations taken in connection with those of Balbiani, 

 Van Bambeke, and other earlier workers give, however, strong evidence, 

 as I believe, that the 'yolk-nucleus' of Lumbricus is derived, if not from 

 the nucleus, at any rate from a substance nearly related with chroma- 

 tin, which is afterward converted into cytoplasmic substance. It 

 is certain, in this case, that the appearance of the yolk-nucleus is co- 

 incident with a rapid growth of the cytoplasm; but we cannot suppose 

 that the latter grows entirely at the expense of the yolk-nucleus. More 

 probably the yolk-nucleus supplies certain materials necessary to 

 constructive metabolism, and it is not impossible that these may be 

 ferments. We may perhaps interpret in the same manner the elimina- 

 tion of separate nuclear elements, (i.e., not forming a definite yolk- 

 nucleus) as described bj^ Van Bambeke, Mertens, v. Erlanger and 

 many earher writers. 



