334 KING. [Vol. XVII. 



cell if the cell divisions did not follow each other quite so 

 rapidly. 



After the breaking down of the segmentation nucleus, there 

 are no nucleolar-like bodies found near the spindle, as one 

 would expect to find if some of the rounded masses in the 

 pronuclei were true nucleoli. The entire substance of the 

 segmentation nucleus is either absorbed at once or else it 

 goes into the formation of the spindle. The changes occur- 

 ring at this period take place very quickly, and I have been 

 unable to follow them in all their details. 



Although a definite central body has been found in the 

 attraction spheres of various annelids, mollusks, echinoderms, 

 and vertebrates, as yet it has not been discovered in any 

 unsegmented amphibian Q.gg, even with methods of preserva- 

 tion and staining which have clearly demonstrated its presence 

 in other eggs. Eismond finds condensed portions in the 

 attraction spheres of Triton and Axolotl, which he thinks may 

 be comparable to the centrosome found in other forms. These 

 bodies are not solid, are in no way constant in size, number, or 

 position, and are undoubtedly, as Eismond himself suggests, 

 the result of certain mechanical conditions. Braus ('95) has 

 described typical centrosomes in the many-layered blastula 

 cells of Triton ; but he states that these centrosomes are very 

 difficult to find in the two-layered blastula cells and makes no 

 mention of their existence in the unsegmented eo:g. 



At no period in the fertilization of the ^%g of Bufo is there 

 the slightest trace of a definite central point in the astrospheres 

 from which the rays diverge. The nearest approach to it is in 

 the stage of PI. XXXI, Fig. 56, where the rays seemingly con- 

 verge towards a center ; but this center is never a single gran- 

 ule or a mass of granules ; it always appears to be composed of 

 the massed ends of the radiating fibers. In other stages the 

 reticulum of the astrospheres is perfectly uniform. Therefore, 

 in the ^^g of Bufo, and presumably in other amphibian eggs, 

 either the reagents used in killing and hardening do not pene- 

 trate the egg sufficiently well to preserve the delicate structure 

 of the centrosome, or the mechanism of cell division can be 

 carried on independently of a centrosome, and this structure 



