CELL SIZE AND NUCLEAR SIZE a 
Figs. 20 to 28 show eggs which were centrifuged during the 
second cleavage. The first and second cleavages may always 
be distinguished by the fact that the polar furrow bends to the 
right in the first cleavage and to the left in the second (Conklin 
97). In fig. 20 the distribution of cytoplasm and yolk to the 
daughter cells was equal in the first cleavage but unequal in the 
second, and the daughter nuclei are proportional in size to the 
volume of the cytoplasm in which they lie. 
In fig. 21, which represents an egg which was centrifuged for 
30 minutes and fixed at once, the second cleavage is very unequal, 
two of the macromeres (B and C’) being small protoplasmic cells, 
which resemble micromeres in appearance, but which behave like 
macromeres as the study of later stages (figs. 24 to 28) shows. 
Fig. 22 represents an egg which was centrifuged for thirty 
minutes during the second cleavage and then kept under normal 
conditions for twenty-one hours before being fixed. ‘The second 
cleavage was suppressed although the nucleus divided in the upper 
cell, AB, but not completely in the lower one, CD. These nuclei 
have given rise to spindles for the third cleavage, there being two 
independent spindles in the cell AB, and two spindles which are 
fused at one pole in the cell CD, thus forming a triaster. The 
degree of abnormality in this case is indicated by the fact that 
the development has been halted at this stage, although a normal 
egg would have reached the 20-cell stage at least, in the time which 
elapsed after centrifuging. 
With the exception of fig. 26, all of the figs. from 23 to 28 were 
drawn from the same lot of eggs which were centrifuged for thirty 
minutes in the 2-cell stage, and then kept for six hours under 
normal conditions before being fixed. In all of these eggs the 
second cleavage was made very unequal by the centrifuging. 
Two of the macromeres are not only much smaller than the other 
two, but are composed entirely of cytoplasm, whereas the two 
larger macromeres contain all of the yolk. Nevertheless the 
behavior of these two small, protoplasmic macromeres is almost 
identically like that of the large, yolk-rich macromeres; the micro- 
meres are given off from both the protoplasmic and the yolk 
laden macromeres at practically the same time and in the same 
