172 TRANSACTIONS OF THE [May 11, 
by the old rays still converging to the old center. The diver- 
gence of the chromosomes is accompanied by a gradual elonga- 
tion of the old spindle, so that the outer periphery of each cen- 
trosphere comes to lie nearer the egg periphery. By the time 
the chromosomes have reached the edge of the centrosphere 
each becomes converted into a minute vesicle, and the centro- 
somes of each amphiaster have further diverged, while their rays 
have increased in number and distinctness. (Fig.17.) The old 
rays are now mostly indistinguishable, though they persist for 
some time on the sides of the former centrosphere, still converg- 
ing to the old center. Boveri has figured (1) just such a per- 
sisting convergence of rays to a previous center, in Ciona, just 
previous to formation of the first cleavage figure. 
The vesicles are now drawn up into the region of the former 
centrosphere, where they gradually fuse, forming at first a lo- 
bate nucleus. The newly formed amphiaster lies on the outer 
periphery of this nucleus, the two asters separated about 90° + 
(Fig. 18.) 
It might be noted that from the first each aster seems to de- 
velop, independent of the other, around its focal centrosome; 
there seems to be no persistent and genuine “ central spindle ” 
connecting them. What seems to be a central spindle in Fig. 
17 is, I believe, merely a transitory, non-significant structure 
due to the meeting of rays from the two asters. It later dis- 
appears, with the complete fusion of the vesicles. 
The nucleus now rounds out, all trace of the component 
vesicles disappearing, while the asters continue to diverge until 
they occupy opposite poles of the nucleus. Even before the 
definite position has been reached, spindle fibres commence to 
grow in toward the nucleus. The subsequent history, so far as 
traced, 7. e., until commencement of the second cleavage ana- 
phase, is but a repetition of that of the first. At the poles of 
the completed vesting nucleus, spindle fibres grow in, folding 
the membrane, which later first fades away at these points. The 
nucleus becomes spindle-shaped; a centrosphere is formed 
around the centrosomes, which very early divide and become 
surrounded by a darker area within the centrosphere. In the 
equatorial plate stage, or slightly later, the centrosomes com- 
mence to migrate toward the outer periphery of the centro- 
sphere, where the dark area fades away. Further than this I 
have not followed it. 
EFrect OF FIXING AGENTS. 
Sublimate-acetic (80% sublimate solution and 20% acetic 
acid), though in general affording fine fixation of both chromatic 
