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STUDIES OF FERTILIZATION 439 
In general, larger sperm nuclei are accompanied by larger 
asters and smaller nuclei by smaller, roughly proportional, asters, 
after they are fully formed. Exceptions to this rule are certainly 
rare. I have, however, found a very few cases, two or three in 
all, in which a’ very small sperm nucleus is accompanied by a 
disproportionately large aster. The explanation of such cases is 
uncertain, but I am inclined to attribute it to a secondary reduc- 
tion of the sperm nucleus after penetration and aster formation, 
such as might conceivably result from some form of injury received 
in centrifuging. 
The significance of this proportional relation is at once apparent ; 
if the aster is a product of a nucleo-cytoplasmic reaction of some 
kind, as we have already seen reason to believe, there must be a 
quantitative relation between the product (aster) on the one hand, 
and the reacting elements (nucleus and cytoplasm) on the other, 
and this is what we find. 
After maturation is completed and the germ nuclei are formed, 
we have to find a new criterion for partial sperm nuclei. Com- 
parison of size of the egg and the sperm nucleus alone is not very 
satisfactory, because both nuclei are swelling very rapidly at this 
time and they may meet and begin to fuse before their enlarge- 
ment is complete, so that complete identity in size of egg and 
sperm nucleus prior to fusion is not invariable in the normal fer- 
tilization. But a valid criterion may be found in the following 
phenomena: the germ nuclei are formed by chromosomal vesicles, 
one for each chromosome, and in each vesicle a sharply marked 
chromatic nucleolus arises before the separate vesicles fuse. Fu- 
sion begins very early and growth of the nucleoli accompanies 
it; however, an elimination or dissolution of the nucleoli begins 
before fusion is complete, so that their number is rapidly reduced 
again, and they entirely disappear before the actual prophases 
of the first cleavage spindle. Fusion of the two germ nuclei 
with one another may also begin before the fusion of the chromo- 
somal vesicles in each is complete. Under normal conditions the 
number of the chromatic nucleoli is probably the same in each 
germ nucleus in the early stages. I therefore looked for cases of 
striking disparity in number between the chromatic nucleoli of 
