352 PROCEEDINGS OF THE ACADEMY OF [April, 
tips in size, which are directed toward the vegetative pole (Pl. XXIII, 
figs. 21, 22, 23, Pl. XXTV, fig. 24). 
The second quartet at this time consists of four similar groups of 
cells, each group consisting of two large cells, 2a?—-2d" and 2a7—2d?}, 
lying together, with the smaller cells above and below. The two large 
cells in all four quadrants, 2a”—-2d”, 2a7-2d"4, next divide almost 
simultaneously. The direction of cleavage of the right upper cells 
(2a"-2d") is dexiotropic, and of the resulting cells the upper (2a’7- 
2d") are slightly larger than the lower (2a'”-2d*), the divisions being 
identical in all four quadrants. Synchronously with these divisions 
cleavage spindles appear in the other large cells of the second quartet 
(2a7*-2d7'). Of the resulting cells the lower are much the smaller. 
In direction the cleavages are probably all leotropic and therefore 
non-alternating, though in C and D quadrants the spindles are almost 
meridional in position, and the cleavages horizontal. Figures 28, 29, 
30, 31 and 32 show these divisions in the different quadrants. 
The lack of alternation found in the above instance may be explained 
as the direct result of the relative sizes of the foregoing derivatives of 
the second quartet and the positions in which they lie. By an exami- 
nation of fig. 30 it will be seen that should the two large cells, 2c and 
2c”!, have divided in the same direction a diagonal row of cells would 
have been the result, with great pressure against one another and upon 
the cells in the first and third quartets at the ends of the row. Lack 
of alternation in direction of cleavage in one of the cells would relieve 
this pressure, and this is the actual condition found. Such an expla- 
nation appears to fit this individual case of non-alternation, but no 
generalization may be made, as in many other instances the cleavage 
of blastomeres appears to follow no rules of mutual pressure and can 
be explained on no grounds so simple. 
Division again occurs in this quartet at a stage of about eighty cells 
and great variation in time is marked in their occurrence. 
The following table shows the average sequence observed in the 
different quadrants, though any one egg may show marked variation 
from the tabulated result: 
