JENNINGS: DEVELOPMENT OF ASPLANCHNA HERRICKII. 37 
where they were given off. (Compare Figure 50, Plate 6, with Figures 
56, Plate 7, and 65, Plate 8.) 
Other changes occur at the same time in the large ventral cell. After 
the fifth cleavage the granular cloud in the cytoplasm gathered into the 
region of the anterior margin of the free surface of the cell (Plate 5, 
Fig. 38). As the spindle for the sixth cleavage is formed, the cloud 
becomes concentrated over a small area, at a slight distance from the 
anterior margin of the cell (Plate 6, Fig. 48). Then, as division takes 
place, the cloud moves up to the anterior margin, at the same time 
spreading out, and begins to pass beneath the cells of the quadrants 4 
and B (Figs. 49 and 50). As the large nucleus moves away from the 
wall of the cell where the vesicle was formed, the granular cloud moves 
inward (dorsad) and spreads out between the nucleus of the large cell 
and the two vesicles (Figs. 51 and 52). The granules at this time have 
become very coarse and distinct. 
Meantime, cleavage is taking place in the cell d9?, In this cell the 
changes occurring in the asters are peculiar. 
Immediately after the preceding cleavage, the cell, having passed 
into the resting stage, has been pressed into an irregular wedge-shaped 
form by the processes occurring in the surrounding cells (Plate 5, Fig. 
37, surface view, and Fig. 38, section, from the same egg). ‘The cell 
has become very narrow at the level at which the nucleus lies, so that, 
apparently, there is not room for the asters to separate at right angles 
to the foregoing spindle. The nucleus is pressed closely against the 
ventral wall of the cell (Fig. 38), and the aster begins to extend 
obliquely along the dorsal side of it, between the nucleus and the dor- 
sal wall of the cell. When the aster has become completely divided 
and the products are on opposite sides of the nucleus, their common 
axis is already in the same direction as the axis of the spindle at the 
previous division. The same result is obtained as in the rotation at the 
fourth cleavage, though in a different manner. But the final positi 
not yet reached. 
As now situated, the asters lie in the long axis of the much elongated 
cell (Plate 6, Fig. 46). As the active condition preparatory to di- 
vision comes on, the cell withdraws its deeper parts (shown in Plate 5, 
Fig. 38), and its dorso-ventral dimension increases. Accompanying this 
change is a rotation of the nuclear complex, from a position with the 
axis in the greatest dimension of the cell, to a position with axis in the 
shortest dimension. This change is shown in progress in Plate 7, 
Fig. 53. A later stage is shown in Figure 54; here the spindle is 
