No. 2.] THE DEVELOPMENT OF THE AEJVT. 293 



deiitogenic substances are formed in the vesicle, perhaps through 

 the agency of the nucleoli, and are then sent forth to share in 

 the building up of the cell. The peripheral position of the nu- 

 cleoli in amphibian eggs, and their subsequent migration to the 

 center after yolk construction has practically ceased may be 

 best explained by supposing that in some way they take part 

 in the management of deutoplasmic affairs. That either the 

 germinal vesicle, as represented by the migrating granules, or 

 the cytoplasm, as represented by the yolk-nuclei, is exclusively 

 concerned in yolk-formation does not seem to me probable. If 

 it be desired to formulate an hypothesis one might suppose 

 that granules from the germinal vesicles serv^e as starting 

 points, centers of attraction or stimulation as it were, while 

 the cytoplasm, perhaps through the mediation of the yolk-nuclei, 

 elaborates and supplies the requisite deutoplasmic material out 

 of nutritive elements furnished it by the follicle cells. 



I may add that there is some support for such a view in 

 the recent cytological work of Macallum ('9l). From studies 

 upon the ovarian ova of Nechtrus and Rana, principally with 

 the indigo-carmine stain, he draws the following conclusion : 

 " The peripheral nucleoli generate a substance, therefore, which 

 diffuses gradually through the nucleus, then into the cell pro- 

 toplasm, the point of time of the latter occurrence correspond- 

 ing with the formation of the yolk spherules. ... I regard 

 the yolk spherules as formed by the union of a derivative of 

 the nuclear chromatin with a constituent of the cell proto- 

 plasm. . . . The formation of yolk spherules in the cell 

 protoplasm is analogous to the formation of zymogen granules 

 in the pancreatic cells, and both are accompanied by changes 

 in the nucleus and an increase in the cell protoplasm. It is 

 most natural to conclude that the processes underlying the 

 formation both of the yolk spherules and of the zymogen 

 granules are in a general way alike." That there is some such 

 sharing of nucleolar substance in cytoplasmic activities as 

 Macallum here avers is a familiar and well-supported 

 opinion. 



Korschelt ('89) thus expresses a widespread conviction : " Ich 

 muss es nach meinen Erfahrungen, die an Eiern und anderen 



