140 T. H. Morgan. 



pieces of the tissue of the body of the same or of another In- 

 dividual I have not laid much stress on this observation, or ac- 

 credited the results to the presence of an exciting substance. At 

 times I have thought that the spermatozoa were more active 

 around the eggs of another Individual than around the eggs of the 

 same Individual, but as there Is no very accurate means of determin- 

 ing their relative motility, unless very marked, I should not wish, 

 as yet, to give a final answer to this question. It is certain that there 

 Is no such great difference In the behaviour of the spermatozoa 

 In the presence of the eggs of the same and of another individual 

 as to suggest that the difference In the result Is connected with this 

 factor. And even if this were the case, the Influence probably 

 extends for only a short distance from the surface of the egg, as 

 the following experiment shows. 



The eggs were taken from the oviduct, great care being taker 

 not to injure the sperm-duct. The eggs from another Individual 

 were collected In the same way. An equal number of eggs from, 

 each were put together and fertilized with the sperm from one 

 of the individuals. In another dish another lot of the same eggc 

 were mixed half and half, and these fertilized with the spern 

 from the other Individual. In each of these two sets half at 

 least of the eggs should be fertilized by the other sperm, but half 

 should not be fertilized unless the eggs of one Individual exer. 

 some Influence that causes the sperm to fertilize the eggs of the 

 same individual also. It was found that only about half of the 

 eggs were fertilized. This result shows that the fertilization I 

 probably not due to some substance set free by the eggs that act? 

 on the sperm or at least that if such a substance is set free Its 

 action Is confined to the Immediate vicinity of the egg. The 

 experiment does not show, however, whether the egg, or its 

 membranes, may not contain some substance that prevents the 

 spermatozoa from entering the eggs of the same Individual. Ever 

 If such a substance Is set free from the eggs it may not have had 

 time In my experiment to accumulate sufl'iclently In the surround- 

 ing water to have prevented the spermatozoa from fertilizing the 

 other eggs, which may be quickly entered. This view can be 

 tested by letting eggs stand In a small amount of water for c 



