H. M. FucHS 269 



fertilization by their " own " sperm, i.e. by sperm from the same indivi- 

 dual. It was thought that if there were such a substance, its presence 

 in the sea-water should prevent sperm taken from the same individual 

 as itself from cross-fertilizing the eggs of another individual. That 

 such is not the case is demonstrated by the experiments shown in 

 Tables II and IV, in which the extracts were taken from the same 

 individuals as those from which the sperm was derived. These extracts 

 caused an increase in the number of eggs fertilized in their presence. 



It might be, however, that an egg-extract from the same individual 

 as the sperm had a lesser stimulating effect than one from a " foreign " 

 animal. In the much smaller concentration in which the substance 

 must be present at the surface of eggs in the sea than in artificial egg- 

 extracts, "own" extract might have no perceptible favouring influence 

 on fertilization, while the influence of that from another individual 

 would be great enough to be effective. In this way, the difficulty of 

 effecting self-fertilization could be accounted for. 



The h3rpothesis was put to the test in the following experiment. 

 Approximately equal amounts of ^ eggs were put into (1) 10 cc. water, 



(2) 10 cc. of egg-extract derived from the same animal as the eggs (A), 



(3) 10 cc. of egg-extract derived from the same animal as the sperm (B), 

 and (4) 10 cc. of extract derived from a " foreign " animal (C). After 

 35 minutes, one drop of b sperm-suspension was added to each dish. 

 It should be noted that the three extracts were made as nearly as 

 possible of equal concentration. 



The Table shows that the extracts derived from the three indivi- 

 duals had practically the same stimulating effect on fertilization. The 

 difference of 17o li^s within the limits of experimental error.- 



The foregoing experiments show that self-sterility in Ciona cannot 

 be accounted for by the presence of a substance in the eggs of an 

 individual B, which not only prevents the union of B eggs with 

 b sperm, but also of "foreign" eggs (A) with b sperm. Nor is it due 

 to something contained in B eggs which favours fertilization of eggs A 

 by b sperm relatively less than does a substance contained in the 

 " foreign " eggs. At any rate, if such an inhibiting substance be 

 present, its effect is masked by stimulating substances contained in 

 the egg-extracts. 



