FORMATION OF POLAR SPINDLE IN BUFO. 83 



ments " and are carried to the "plage fusoriale " where they 

 either become vacuolated in the center and form a rincf, or else 



o * 



they fuse into one large mass and later regain their individuality. 

 \Yhen the spindle is first formed, the chromosomes are very ir- 

 regular in shape and there are distinct asters at the spindle poles 

 which never contain a centrosome. 



In the egg of Bnfo lentiginosus, I have traced the chromo- 

 somes of the germinal vesicle up to the stage where the ends of a 

 pair of chromosomes unite to form a closed ring. After this 

 time, although I have had an abundance of material and have 

 searched very carefully through every section of the germinal 

 vesicle in a large number of eggs, I have been unable to find 

 any trace of the chromatin. There is, I believe, no doubt but that 

 the chromatin rings break up into minute granules which may, pos- 

 sibly, be carried by the karyoplasmic radiation to the lower pole of 

 the germinal vesicle where they later form the chromosomes of 

 the first polar spindle. I have never seen anything in this egg, 

 however, that would indicate that some of the tutcleoli are destined 

 to form the chromosomes of the first polar spindle. A large 

 number of nucleoli are always present throughout the early stages 

 of maturation and they all appear to be undergoing the same 

 processes of disintegration. Carnoy and Lebrun might consider 

 the large irregular masses shown in Fig. 2 to be nucleoli in the 

 general sense in which they seem to use the word, but these 

 masses have been formed by the fusion of smaller chromatin 

 granules (Fig. i) and are in no way connected with the true 

 nucleoli of the germinal vesicle. 



Carnoy and Lebrun have followed the details of the formation 

 of the first polar spindle and the later changes of the chromo- 

 somes much more carefully in the egg of Triton than in any of 

 the other amphibian eggs they have studied. Their account of 

 this form agrees substantially with that of Bnfo vnlgaris as re- 

 gards the breaking down of the germinal vesicle, with the im- 

 portant exception that in Triton, all of the nucleoli are absorbed 

 by the cytoplasm, none of them are reserved, as in Bnfo Vnlgaris, 

 to form the chromosomes of the first polar spindle. The chro- 

 matin threads which were resolved from the nucleoli at an earlier 

 period, break up into very small granules when the membrane 



