382 FRANK R. LILLIE 
gone maturation, prove that the unsegmented eggs had received 
at least the first stimulus of fertilization. It was also shown that 
the critical period for suppressing segmentation by centrifuging 
occurs at a time shortly before entrance of the spermatozoon, and 
that it is due to prevention of penetration. The partially fer- 
tilized eggs, therefore, resemble the normal ones in the fact that 
membrane formation and the first stimulus to development are 
called forth by action of the spermatozoon, and they differ from 
the normally fertilized eggs in that the internal egg protoplasm has 
not received the direct stimulus of the spermatozoon. A cyto- 
logical examination of such eggs could not fail to be of interest 
and might give some clue to the internal function of the spermato- 
zoon in fertilization. 
Both polar bodies form regularly in such eggs as already noted, 
and the egg-nucleus (female pronucleus) arises and attains the 
same size as in normally fertilized eggs. The chromosomes of the 
first cleavage spindle then form in the usual fashion and at 
the usual time, accompanied by disappearance of the nuclear 
membrane. But, whereas, in the presence of a sperm nucleus, 
cytoplasmic asters accompany these processes and a spindle 
rapidly arises during the prophases of the first cleavage, in the 
absence of the sperm nucleus there is absolutely no sign of cytas- 
ters or evidence of spindle formation. The chromosomes lie 
naked in the cytoplasm surrounded by a clear area (fig. 7). 
Each chromosome then splits longitudinally in the usual 
fashion, but the halves do not separate. At the time of the 
telophase of the normal first cleavage there is a tendency to 
scattering and breaking up of the chromosomes. When the nor- 
mal eggs have reached the two and four-celled stages, the scat- 
‘tering and breaking up of the chromosomes have progressed 
much farther in the unsegmented eggs, and in the course of two 
or three hours there remains no differentiated nucleus or chro- 
mosomes, but only numerous chromatic granules scattered 
throughout the cytoplasm. 
The behavior of the partially fertilized eggs may be compared 
on the one hand with that of normally fertilized eggs and on the 
other with that of eggs caused to mature by centrifuging. As com- 
