-328 T. H. MORGAN. 



12. Extracts of the sperm of other individuals did not, in the 

 few cases tried, induce self-fertilization. 



i 3. Dilution of the sea water does not facilitate self-fertilization, 

 although cross-fertilization may still occur in water considerably 



diluted. 



14. Eggs after standing for 24 hours in sea water are not fer- 

 tilized by their own sperm. 



15. Bursting the eggs, so that the membrane is ruptured or 

 the egg is set free, allows self-fertilization to occur in a large 

 number of cases, showing that the lack of self-fertilization of the 

 unbroken egg is probably due to a resistance found in the sur- 

 face of the egg, in the membrane, in the follicle cells or in their 



secretions. 



HYPOTHETICAL AND SPECULATIVE. 



The immunity of the eggs of dona to its "own " sperm invites 

 a comparison with cases of immunity to infectious diseases. The 

 more so since Landsteiner and Metschnikoff have found that 

 when, for example, spermatozoa of the ox are injected into the 

 guinea-pig they remain active for some time, but if the injections 

 of the ox sperm are continued at proper intervals the guinea-pig 

 makes a spermatoxin that quickly brings to rest all later-injected 

 spermatozoa. If something similar occurs in dona the reaction 

 is much more delicate than any heretofore discovered, and would 

 open a wide field for future investigation. 



Without wishing at present to press this point too far it seems 

 to me of sufficient weight to warrant calling attention to some of 

 the implications in the case of dona. 



The presence of eggs and sperm in the same individual might 

 appear to give an opportunity for a reaction similar to that just 

 described. If the eggs, and also the body tissue of the animal, 

 were supposed to make a counter substance that would bring the 

 spermatozoa to rest, we might account for the lack of self-fertili- 

 zation in this way. Further, the proximity of the sperm-duct 

 and the oviduct in dona suggests that the eggs might all the 

 more easily be stimulated to form the substance. 



There is also another possibility, viz., that a substance may be 

 secreted by the sperm-duct that keeps the mature spermatozoa 

 at rest, and that this substance may affect the near-lying eggs, so 



