No. I.] POLYCHOERUS CAUDATUS. 87 



to shorten the speckled rays from the centrospheres with 

 which it comes in contact. In Fig. 1 1 it will be seen that 

 these rays extend directly to the nuclear membrane ; in Fig. 1 2 

 they are much shorter, while in Fig. 13 they have disappeared 

 on the sides directed toward the nucleus. 



As the achromatic fibers are thus being formed from the 

 linin, that portion of the nucleus which lies directly between 

 the two centrospheres undergoes differentiation. The par- 

 ticles of chromatin collect to form irregular clumps (Fig. 13) 

 imbedded in clear linin. It looks as if the linin in flowing 

 out toward the aster centers had brought the chromatin par- 

 ticles into contact with one another, and that these gradually 

 melt together to form solid masses. 



At first these masses show distinctly that they are made up 

 of separate chromatin granules (PI. XI, Fig. 29), but as the 

 amphiaster develops the particles knit together, and as the 

 achromatic rays begin to differentiate out of the amorphous 

 linin, these clumps become elongated into irregular rod-shaped 

 structures (PI. X, Fig. 14, PL XII, Fig. 36). The number of 

 clumps or rod-shaped masses formed is by no means constant. 

 The manner in which the chromosomes are afterwards formed 

 from them will be described later. As these rod-shaped masses 

 are formed the whole amphiaster moves away from the broken 

 nucleus which remains in the center of the ovum. Fig. 14 

 shows this process. From the various positions in which I 

 have seen this amphiaster relative to the remnant of the 

 nucleus, I am inclined to believe that one of the aster centers 

 remains stationary as a pivot and that the other aster swings 

 through a wide arc of nearly, if not quite, 180°, thus freeing 

 the whole structure from the nucleus, and leaving the spindle 

 free to move towards its destination, the surface of the ovum, 

 which it does by moving very nearly in a straight line. The 

 fact that one side of the nucleus is intact in outline (Fig. 14) 

 while the other is completely destroyed bears out this view. 

 Also, at this stage numerous fragments of the nucleus are 

 scattered throughout the cytoplasm, particularly in the neigh- 

 borhood of the broken side of the nucleus. When this is the 

 case the whole cytoplasm stains more deeply than otherwise. 



