196 Experime7ital Zoology 



to inability to enter the ^gg, and not to failure of the develop- 

 mental process after fertihzation. 



If the spermatozoon 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 ^%% to receive the proper stimulus to 

 take in the spermatozoon; 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 fertihzed 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 fertihze 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 ^gg^ or is due 

 to the failure of the egg to respond to the stimulus of its own 



