320 KING. [Vol. XVII. 



staining rounded masses in the pronucleus are composed of 

 chromatin or whether some may not be newly formed nucleoli. 

 The enormous volume of these bodies as compared with that of 

 the chromosomes which went into the formation of the pro- 

 nucleus, would seem to favor the second alternative ; but the 

 question cannot be settled definitely, because these structures 

 all stain alike, and it is impossible to differentiate them at any 

 stage in the history of the pronucleus. 



6. Nature of the Nucleoli. 



The germinal vesicle of all amphibian eggs contains a large 

 number of nucleoli whose function is not known with any 

 degree of certainty. After describing the disintegration of the 

 nucleoli into small granules, Schultze adds : " Man iiberzeugt 

 sich, dass die Kornchen, die ich jetzt wohl Mikrosomen nennen 

 darf, allmahlich zur Erzeugung eines Fadenknauels zusammen- 

 treten, der also nicht aus einem praformierten Kerngeriist 

 entsteht, sondern sich direkt aus den winzigen Keimkorper- 

 chen herausbildet." This view was completely overthrown by 

 Born's discovery that the chromatin threads in Triton are dis- 

 tinctly traceable througjiout the whole history of the germinal 

 vesicle, existing before, as well as during, the migration of the 

 nucleoli towards the center of the vesicle. 



The general opinion of the nature of the nucleoli in all eggs 

 seems to be that these bodies either represent some kind of a 

 reserve substance as maintained by Pfitzner ('83), Rhumbler 

 ('93), and Korschelt, or that they are a secretion product of the 

 nucleus. The latter view was first advanced by Leuckart ('53), 

 and has since been advocated by Flemming ('80), Hacker ('93, 

 '95), and Wheeler ('97). 



There are at least three different kinds of nucleoli in the 

 germinal vesicle of the toad's ^gg : the very large vacuolated 

 bodies appearing during the hibernation period, which are 

 slowly absorbed without any apparent change in their struc- 

 ture ; the large nucleoli which break up into small yellowish 

 refractive granules before disappearing ; and the minute homo- 

 geneous nuclear bodies which are apparently unchanged when 



