96 BULLETIN: MUSEUM OF COMPARATIVE ZOÜLOGY. 
The other thirty cells show a regular arrangement. The four quadrants 
may be distinguished as at the beginning of the fifth cleavage, each 
quadrant now containing eight cells, showing a characteristic arrange- 
ment. From ventral to dorsal we may now distinguish five layers. The 
first three layers contain each eight cells, two from each quadrant. In 
the quadrants A, B, and C, the two cells of a given layer are equal 
(Plate 6, Fig. 47). In quadrant D there is great irregularity. The 
two cells of the ventral layer are extraordinarily unequal, constituting 
the large partly interior cell de, and the minute vesicle de., also 
enclosed within the other cells (Plate 5, Fig. 38). In the second 
and third layers the two cells are likewise unequal, though less 
markedly so. 
The fourth layer consists of a single large cell from each quadrant, 
that of quadrant D being the largest (Plate 6, Fig. 45). 
The fifth layer consists of four small cells at the dorsal pole of the 
egg (Fig. 45). The arrangement at the animal pole formed at the four- 
cell stage (Fig. 8) is still maintained. The quadrants Band D are in 
contact for a considerable distance, whereas A and C do not touch. In 
one of the points where three cells of different quadrants meet (in this 
case 095, £95, and des) Ties the polar cell. 
The first cells in which indications of cleavage are observed are again 
the large cells of the D quadrant, d?" and d°°. Spindles are formed in 
these at about the same time (Plate 6, Fig. 48). The processes taking 
place in the two cells differ, and must be considered separately. 
[AUNT 
Pit 
In d, after the giving off of the small vesicle d“, the nucleus very 
quickly enlarges to its original size. The aster begins to elongate at 
right angles to the position of the previous spindle (Plate 5, Fig. 38). 
But at almost the same time a rotation takes place, and by the time 
the two asters are fully separated the line connecting them is seen to 
be nearly antero-posterior (Plate 5, Fig. 42). The movement continues 
until the axis of the complex becomes exactly antero-posterior, and a 
spindle is formed in precisely the same position as the spindle for the pre- 
ceding eleavage, This spindle is shown in the sagittal section, Figure 
48. Its anterior end lies just ventrad of the small vesicle formed at 
the previous cleavage. Division now takes place, and a second small 
vesicle is given off to the point in the median plane lying just ventrad 
of the vesicle formed at the fifth cleavage. Figure 49 shows the pro- 
cess of formation of this vesicle, and Figure 50 shows the condition of 
affairs after the division is finished. In later stages the two vesicles are 
visible, lying beneath the cells of quadrants A and , in the place 
