33O T. H. MORGAN. 



Violently shaking the eggs may remove entirely, or in part, 

 the protecting covering, so that self-fertilization may more often 

 take place. 



If eggs are shaken in sea water, so that pieces of the follicle 

 cells are set free, these pieces would bring to rest all of their 

 " own " sperm that came into contact with them, but the number of 

 spermatozoa in the water might be too great for all of them to be 

 caught, and those that remained might suffice to fertilize the eggs 

 of another individual if they were then added to the water. Thus 

 we can see why in the experiments cross-fertilization was not 

 prevented when the sperm was first added to its own follicle water. 



The fact that cross-fertilization was so often incomplete in the 

 San Diego form, and so much more frequent in the form from 

 Woods Hole, suggests that the difference may be due to the 

 closer relationship of the former group of individuals. The 

 Woods Hole individuals were collected over a wider area, and 

 other conditions at this place make it more probable that these 

 individuals may have had a separate descent. The close resem- 

 blance, in fact, between the infertility of dona when self-fertilized, 

 and the infertility of closely inbred forms is apparent, and the 

 same explanation may apply to both cases. 



The immunity of the eggs of Ciona to sperm of the same in- 

 dividual suggests a comparison with the cases of immunity to in- 

 fectious diseases, but it is evident that the two cases can not be 

 identical, for the antitoxin of disease is supposed to combine with 

 the toxin of the poison, and thus inhibit its action. It would be 

 absurd to suppose that there are bodies in the egg large enough to 

 lock up, as it were, the spermatozoa ; but on the other hand it is 

 not impossible that substances may exist that quiet the activity of 

 the spermatozoa, and that these substances are a part of, or the 

 immediate product of, the protoplasm .of the individual, and are 

 not produced by a reaction between the body tissues (or the eggs) 

 and the spermatozoa of the same individual, as in the case men- 

 tioned above when the sperm of one animal is injected into 

 another. 



