80 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
accurately interpreted from observations on the opaque living egg, but 
sections of ova killed at various stages in the cleavage show some in- 
teresting conditions. About the time when the pronuclei come into 
contact, two clear areas are often seen near the pronuclei, as shown in 
Figure 20 (Plate 2), but frequently in a plane more nearly transverse 
than that in which they are shown in the figure cited. In the same 
positions well-defined asters later make their appearance, and the first 
cleavage spindle begins to form with its axis oblique to that of the vitel- 
line membrane (Fig. 21). In many cases the spindle begins to form in 
a plane almost perpendicular to the long axisof the ovum. This is true 
particularly in L. fascicularis (compare Plate 11, Fig. 98). 
In the metaphase of the mitosis the spindle is usually oblique to the 
long axis of the ovum (Fig. 22); sometimes it is almost transverse 
(Fig. 98), but never parallel to the long axis. In L. fascicularis it is 
most frequently perpendicular to the chief axis, as shown in Figure 
98. In L. anatifera the spindle is usually almost as long as the trans- 
verse axis of the ovum. The astral radiations are very distinct, and 
appear to be continuous with the general protoplasmic reticulum of the 
cell (Fig. 22). In the stage of the living ovum corresponding to this 
the yolk has taken an eccentric position at the vegetative pole (Fig. 7). 
The relation seen to exist between the yolk and the aster nearest the 
vegetative pole (Fig. 22) suggests that the movement of the yolk to the 
eccentric position has some relation to the formation of the aster, for 
it is during the development of that structure that the yolk moves to 
the eccentric position. 
In the next stage figured, an sii anaphase (Plate 3, Fig. 23), the 
spindle is still oblique and the cleavage furrow has not begun to form. 
The chromosomes have separated along a plane which is usually inclined 
to the plane in which the cleavage furrow later appears. This stage 
corresponds to a stage of the living ovum which is slightly later than 
that represented in Figure 7. 
Figure 24 represents a stage in the anaphase after the cleavage fur- 
row has become well developed, and the dividing ovum has. begun to 
rotate. This is the condition in stages of the living egg corresponding 
to those shown in Figures 10-13. The central part of the spindle is 
almost perpendicular to the plane of cleavage, but there is a distinct 
bend in the spindle near either end. These bends may be regarded as 
evidence of torsion. Comparing Figures 23 and 24, it appears that 
during division there has been some shifting of the egg substance with 
reference to the spindle, which is at first somewhat oblique to the plane 
