GROWTH AND DIFFERENTIATION OF THE GERM-CELIS 121 



yolk-nucleus is nearly related with chromatin, if not directly derived 

 from it. 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 even 

 after the yolk-nucleus has quite separated from the nuclear mem- 

 brane. Later, however, as the yolk-nucleus breaks up, it loses its 

 nuclear staining power, and stains red like the cytoplasm. 



This conclusion is, however, disputed in a later work by Foot ('96), 

 who maintains that the yolk-nucleus in Allolobophora is not of nuclear 

 but of " archoplasmic " origin, though no relation between it and an 

 attraction-sphere is established. ^ She adds the very interesting dis- 

 covery that the " polar rings " (cf. p. i 50) are probably to be identi- 

 fied with the yolk-nucleus, or are at least derived from a similar 

 substance. 



Calkins's observations taken in connection with those of Balbiani, 

 Van Bambeke, and other earlier workers give, however, strong evi- 

 dence, as I believe, that the "yolk-nucleus" of Lmnbriciis is de- 

 rived, if not from the nucleus, at any rate from a substance nearly 

 related with chromatin, which is afterwards converted into cyto- 

 plasmic substance. It is certain, in this case, that the appearance 

 of the yolk-nucleus is coincident with a rapid growth of 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 impo.s- 

 sible that these may be ferments. We may perhaps interpret in 

 the same manner the elimination of separate nuclear elements {i.e. 

 not forming a definite yolk-nucleus) as described by Van Bambeke, 

 Mertens, v. Erlanger, and many earlier writers. 



The meaning of the yolk-nuclei of purely cytoplasmic origin is 

 very obscure, and we have at present really no ground for assigning 

 to them any particular function. It can only be said that their 

 appearance coincides in time approximately with the period of great- 

 est constructive activity in the cytoplasm, but there is no evidence of 

 their direct participation in the yolk-formation, and we do not know 

 whether they are active constructive physiological centres, or merely 

 stores of reserve substances or degeneration-products. 



1 Miss Foot's use of the term "archoplasm" largely deprives the word of the definite 

 meaning attached to it by Boveri. To identify as "archoplasm" everything stained by 

 Lyons blue is indeed a broad use of the term. 



