494 
ZOOLOGY: E. G. CONKLIN 
zation, this influence does not go so far as to cause the polar bodies to 
develop, even though such polar bodies may be formed several hours 
after the spermatozoon enters the egg. In Crepidula the second polar 
body is formed about three hours after the entrance of the spermato- 
zoon into the egg, and during this time the sperm head has grown into 
a vesicular nucleus and the sperm aster has become quite large, but in 
spite of this the spermatozoon has not sufficiently affected the egg sub- 
stance to cause the second polar body to develop even though that body 
may contain the larger part of the egg protoplasm. Only that portion of 
the egg develops, in such cases, in which the sperm nucleus and aster 
are present. 
This conclusion is similar in many respects to that reached by Zeigler 
(1898) who found that when eggs of the sea urchin. Echinus microtuher- 
culatus, were constricted by cotton fibers under pressure only that 
portion of the egg which contained the sperm segmented while the por- 
tion containing the egg nucleus never divided, though its nucleus fre- 
quently went through the division phases, but without any division 
resulting. In this case the portion of the egg containing the sperm 
might remain for some time connected with the other portion by a 
narrow neck, and yet the influence of the sperm in the one hah did not 
cause the other half to develop. 
These facts are of interest because of their bearing on the nature of 
one of the processes concerned in fertilization. In a series of important 
and extensive works on artificial parthenogenesis and fertiHzation which 
he has summarized in a recent book Loeb (1909) has shown that at 
least two factors are involved in artificial parthenogenesis, (1) an external 
factor, such as butyric acid, which causes a cytolysis of the cortical layer 
of the egg followed by increased oxidation and which leads to the rapid 
disintegration of the egg at normal temperatures, and (2) an internal 
factor, such as hypertonic solutions, lack of oxygen, etc., which inhibits 
this disintegration. Loeb concludes that in normal fertilization also 
both of these factors are present and that the spermatozoon carries 
substances into the egg which (1) cause cytolysis of the cortical layer 
and increased oxidation and also other substances which (2) inhibit 
this cytolysis before it leads to the disintegration of the egg. 
My experiments on the giant polar bodies of Crepidula show that 
changes in the cortical layer which prevent the entrance of a second 
spermatozoon take place very rapidly over the entire egg, but that the 
spermatozoon which enters does not cause any portion of the egg to 
develop except the cell in which it hes. Although the spermatozoon 
enters the egg of Crepidula about three hours before the formation of 
