4492 FRANK R. LILLIE 
is considerable variation in such cases in the size of the second 
polar body and the quantity of the chromatin which it contains, 
and corresponding differences in the number of chromosomes 
left in the egg. But the degree of development of the monaster is 
not a function of the number of chromosomes in the egg; and there 
are cases in which no aster formation is associated with a larger 
number of chromosomes in such eggs, and a well developed mon- 
aster with a smaller number. It is possible that there may be a 
qualitative relation depending on what chromosomes are extruded 
in the second polar body; but in view of the complicating consider- 
ations resulting from possible injurious effects of centrifuging 
itself, no definite conclusion on this point seems possible. 
It is, in any event, certain that the sperm nucleus is absent in 
both the second and third classes of eggs. 
As regards the effect of the partial sperm nuclei on the cleavage 
process we are therefore reduced to the class of cases in which a 
cleavage spindle is actually formed. In observing the living eggs 
I was struck with the fact that the cleavage of many centrifuged 
eggs tends to be irregular or partial, especially of those centri- 
fuged at the time when injuries to the spermatozo6n were to be 
expected. And in the sections I find many eases of partial cleayv- 
age. The cleavage of many also stops in the two-cell stage. It 
is natural to suppose that such partial cleavages are the result 
of fertilization with partial sperm nuclei, seeing that we know 
from the data recorded above that there is not even the least 
indication of cytoplasmic cleavage in the entire absence of the 
sperm nucleus. <A rigorous demonstration of such a conclusion 
would, however, require a cytological analysis in which the num- 
ber of chromosomes in the different cleavage spindles of normal 
and partially segmenting eggs should be compared; the relative 
sizes of the karyokinetic figure, and possibly other data, should 
also be taken into account. Unfortunately, the material pre- 
served for this study is in too advanced a stage to make an exhaus- 
tive study of these relations, and this part of the investigation 
must therefore be postponed. 
It must be admitted that other causes than fertilization with 
partial spermatozoa might be responsible for the partial cleavage, 
