196 Experimental Zoology 
to inability to enter the egg, and not to failure of the develop- 
mental process after fertilization. 
If the spermatozoén succeeds in entering, as it does in excep- 
tional cases, the egg develops normally. It is possible by exciting 
the spermatozoa to unusual activity to cause them to enter the 
eggs of the same individual, and these develop. The failure, 
then, is due to the spermatozoa being unable to overcome 
some resistance met with in attempting to enter their “own” 
eggs. There is some evidence that the failure is due to some- 
thing in the egg or its membrane that lessens the activity of its 
“own” spermatozoa that come into contact with it, or pos- 
sibly to a failure of the egg to receive the proper stimulus to 
take in the spermatozoén; but if the latter, it is difficult to 
understand how exciting the sperm to greater activity should 
cause it to enter. 
It is not possible to make the egg receive its own sperm by 
immersing it in the blood or extracts of the ovary of another indi- 
vidual. Conversely, it is not possible to make the sperm enter 
its “own” eggs by soaking it first in the blood or testis-extract 
of another individual. Allowing the eggs of an individual to 
stand for some time in sea water, so that any substance they 
excrete may be set free, and then placing the eggs and sperm of 
another individual in the same water, does not lead to self- 
fertilization. This experiment shows that the results are not 
due to soluble substances set free by the egg causing the egg to 
become fertilized by the sperm of another individual. Con- 
versely, if the eggs of an individual are soaked for some time 
in sea water, and then sperm of the same individual is added in 
the same sea water and later the eggs of another individual are 
added, they will be fertilized. This result shows that the eggs 
do not set free a substance that brings to rest their own sperm, 
for, as shown in the experiment, the sperm will fertilize other 
eggs, if they are added to the solution. These and other ex- 
periments show that whatever the nature of the result, it is 
brought about by some insoluble substance in the egg, or is due 
to the failure of the egg to respond to the stimulus of its own 
