H. M. FucHS 257 



some time after having been deposited, the eggs are no longer in 

 the presence of the concentrated "own" sperm, which has become 

 diffused in the surrounding water and washed about by waves and 

 currents. In allowing an animal to deposit eggs and sperm when 

 isolated in a small dish, the conditions are quite otherwise, for the 

 water into which the eggs are deposited becomes at the same time 

 charged with spermatozoa. The latter can subsequently self-fertilize 

 the eggs, to a greater or less extent according to concentration and 

 individual capacity, when the optimum time has been reached. 



The cause of self-sterility is hardly touched upon in this investi- 

 gation. The search for a cause led to the investigation of substances 

 secreted by eggs into sea-water. The results of this work form the 

 substance of a separate Part, which, however, deals with cross-fertili- 

 zation alone. So many points had to be settled with regard to the 

 effects of the egg-secretions on spermatozoa used to effect ordinary 

 cross-fertilization in Giona and other forms, that hardly any self-fertili- 

 zation experiments had been made. It is therefore really premature to 

 discuss possible means by which self-sterility is brought about. The 

 experiments detailed in Section IV above indicate, however, that one of 

 the factors may be a change set up in the egg by contact with sperma- 

 tozoa of the same individual — a change which inhibits the entrance of 

 such spermatozoa, and also, although to a much lesser degree, hinders 

 the entrance of " foreign " spermatozoa. 



As is well known, Darwin (5) first made a thorough investigation of 

 the effects of self-fertilization on the offspring, showing that in flowering 

 plants such offspring are not in general so vigorous as those derived 

 from cross-fertilization. In Giona this effect of self-fertilization was 

 veiy striking. As has been shown above, the early segmentation is not 

 usually slower in self- than in cross-fertilized eggs. It is interesting to 

 note also that there is no difference in the segmentation rates of self- 

 fertilized eggs from different parts of an oviduct, although the various 

 lots may show quite different capacities for self-fertilization. The later 

 segmentation of self-fertilized eggs is usually a little slower than that 

 of cross-fertilized. In a few cases the larvae failed to hatch well, that 

 is to say, they had difficulty in breaking out of the egg membranes, but 

 this was not usually the case. In many cultures derived from self- 

 fertilizations the larvae failed to settle down after their free-swimming 

 period, but in most instances they settled down in the same way as 

 those from cross-fertilizations. It was after the settling down and 

 metamorphosis, however, that the marked effect usually showed itself. 



Journ. of Gen. iv 17 



