32 BULLETIN : MUSEUM OF COMPAKATIVE ZOOLOGY. 



ing section, Figure 32, it is seen that with the formation of the spindles 

 in d^-'^ and d^-^ these cells have yielded to the well known tendency to 

 take a more rounded form at the time of karyokiuesis; the inner parts 

 of the cells have been withdrawn toward the surface and used in in- 

 creasing the dorso-ventral dimensions of the cells. The animal pole 

 has been thereby pushed still farther in the direction in which it has 

 been steadily migrating, so that it is actually past the microraere end of 

 the egg. The cells of the quadrants A, B, and C, being in a "resting" 

 condition, give way to the compression, and become much deeper and 

 flatter than before. The cell d^'^ retains its position at the macromere 

 end of the egg, but lying iu a concavity, partly surrounded by the 

 other cells. The spindle lies in the deeper (more dorsal) parts of the 

 cell, with its right end (Fig, 33) deepest, and close to the wall of 

 the cell. A view from the ventral end of the eg^^ (Plate 5, Fig. 35) 

 shows that this " right" end is really anterior, and that the spindle lies 

 in an antero-posterior plane, coincident with the plane separating the 

 quadrants A and B. The anterior (inner) end of the spindle lies close 

 against the boundary between a^'^ and iP-^, 



The division which now ensues is of an extraordinary character. The 

 anterior end of the spindle is pressed against the periphery of the cell 

 at the place above mentioned, and a minute vesicle is given ofiF, which 

 lies embedded between the cells a^-^ and J^"\ This, after the division 

 is finished, is shown in Figure 38 (Plate 5), the vesicle being 

 labelled d^-\ 



During division, the granular cloud which was described as occupying 

 the antei'ior half of the periphery of the cell moves still farther toward 

 the anterior margin, and shows a tendency to concentrate into a more 

 definite group ; the individual granules become larger also (Fig. 38). 



In d^-"^ and d^-^ the spindles are parallel to the spindle in c?^*\ the 

 right ends being nearer the boundary of the cells, and deeper within 

 the Q^g. The latter fact is shown in the transverse section, Figure 36, 

 passing through the cells of the third layer. The divisions are un- 

 equal, as foreshadowed by the position of the spindles, but the inequality 

 is much less than in the case of d^-^. The completed division is shown 

 in Figure 37. The cleavage takes place first in d^'^. 



At about the same time as the division of d^-^ occurs that of the dor- 

 sal cell, d^-*. Here the spindle is in the short axis of the cell ; the 

 cleavage is equatorial and unequal, the dorsal cell being much the 

 smaller (Fig. 37). 



During the occuiTence of the cleavage of these cells other changes, 



