312 KING. [Vol. XVII. 



finally there is formed a mass of small round bodies (Fig. 12, 

 D) which, for a time, lie scattered in the substance of the vesi- 

 cle, but which have completely disappeared by the time the 

 segmentation spindle is formed. 



The twelve pairs of chromosomes can be traced through- 

 out all the changes that have been described. They shorten 

 gradually and become proportionally thicker, still, however, 

 showing a distinct microsome structure. When the nuclear 

 membrane disappears, the pairs of chromatin threads are 

 scattered over a considerable area, and the ends of each pair 

 have fused completely, so that twelve closed chromatin rings 

 are formed (PI. XXVIII, Fig. 8, F). These rings apparently 

 have no connection with the line of radiation or with the radi- 

 ation itself. When the line of radiation is beginning to de- 

 crease in length there suddenly appears near each chromatin 

 ring a small, well-defined aster (PI. XXIX, Fig. 24) in which 

 the delicate rays converge towards a central part seemingly 

 composed of only the ends of the astral rays united into a 

 closed meshwork. Iron-haematoxylin with all methods of fixa- 

 tion fails to disclose a centriole or any definite body in the 

 center of these asters that might be considered a centrosome 

 according to Boveri's ('88) definition of the word. There may 

 be several asters scattered throughout the nuclear substance 

 which are not connected with chromatin rings, but after the 

 asters have once appeared, no chromatin ring is ever found 

 without one. 



Unfortunately there is a break in my series of preparations at 

 this point, so that I am not able to follow the next changes 

 that occur in the Q.gz?- About one hour after the stage of 

 PI. XXIX, Figs. 21 and 22, the nuclear substance is nearly 

 uniformly distributed throughout the upper hemisphere, and 

 the fully formed spindle, undoubtedly derived from the line of 

 radiation, is found at some distance below the surface of the 

 &g^. The spindle lies in the midst of yolk granules and is not 

 surrounded by any marked accumulation of cytoplasm. Its 



1 During the spring of 1S99, material was obtained giving a complete history 

 of the formation of the first polar spindle. A detailed account of these changes 

 will be published later. 



