KOFOID: DEVELOPMENT OF LIMAX. 55 
cells of the basal quartet (5.1) retain their preponderance, and may still 
be designated as macromeres after this division. 
The cell d”? (somatoblast of Wilson) is not appreciably larger than 
the other members of the quartet to which it belongs. 
Division of Quartet 4.2, forming 5.3 and 5.4. 
Plate III. Figs. 20-235 Plate IV. Figs. 28, 29. 
'The same stages which show spindles in the lower quartet also exhibit 
them in the upper and smaller quartet. The mitosis is not however so 
far advanced as in the lower quartet. The nuclear membrane can still 
(Figs. 20, 21) be traced, though the asters are present, and the axis of 
the spindle can therefore be determined. This, as in the lower quartet, 
is inclined ; however, it is more nearly parallel to the equator than to 
the vertical axis. "The inclination is in the same general direction as that 
of the spindles of the lower quartet, and the conditions of the completed 
division can be inferred as readily from the figures. Viewing the egg 
from the animal pole and passing from tho lower derivative or aster to 
the upper, wo move in a direction opposite to that of the hands of a 
clock, and this spiral, like that of the other quartet of this generation, 
is therefore a left one. This division, like that of the basal quartet, 
results in cells of almost equal size (Plate IV. Figs. 28, 29), the upper 
derivatives in this case (5.4) being, however, slightly larger than the 
lower (5.3). 
The conditions in Figures 20, 21, show that the sixteen-cell stage will 
in this case follow immediately upon the eight-cell, without the inter- 
vention of a well marked twelve-cell stage. There is, however, so much 
variation in the rate of cleavage in Limax, that it might be expected that 
a twelve-cell stage would occasionally make its appearance. We have 
but to increase tho difference between the mitotic conditions of the cells 
of the two quartets of Figures 20 and 21 to produce such a stage. 
Warneck (50) figures in Tafel V. Fig. 46, a twelve-cell stage of Limax 
agrestis, and one egg in this stage has come under my own observation. 
This stage occurs regularly in forms with abundant yolk, as Planorbis, 
Umbrella, ete., but Nereis, like Limax, passes directly from the eight- to 
the sixteen-cell stage. The completed sixteen-cell stage is shown in 
Figure 22, Plate TII., in which the genetic relations of the cells are still 
indieated by the approximated nuclei. 
With the completion of tho sixteen-cell stage and the fifth generation, 
the dorsal and ventral cross furrows are rostored to the conditions of 
