240 Studies in the Phusiohxjji of Fertilizatioti 



Exp. 1, A/a„, Exp. 2, Bjbi, and B/n. The further point which these 

 two experiments were made to test, namely the behaviour of • sperm 

 from different regions of the vas deferens, must remain undecided for 

 the reason that the different suspensions cannot be made up to exactly 

 equal concentrations. In Exp. 1 sperm from the base failed to self- 

 fertilize, while that from the top fertilized the eggs of the same animal 

 to varjing degrees. In Exp. 2 exactly the reverse was the case. 

 Further, the tests of the two sperms in each ex)ieriment with "foreign" 

 eggs showed that the self-fertilizing powi'r went hand in hand with the 

 cross-fertilizing power. Whether, however, the behaviour of the two 

 sperm-suspensions means that there is a real difference between them 

 or whether it is due to a slight difference in the concentrations of the 

 suspensions must remain unsettled. 



The final conclusion to be drawn from the experiments described in 

 this section is that eggs from different regions of the oviduct have quite 

 different self- (and cress-) fertilizing capacities, when treated with equal 

 concentrations of sperm. Whether or not there is a similar difference 

 in the behaviour of th^' sperm is undecided. The varying behaviour of 

 the eggs is in no way correlated with their position in the oviduct, 

 i.e. with their age, and we must therefore conclude that an animal 

 produces eggs which are at one time more and at another less prone to 

 self-fertilization. 



IV, The Effect of x Sperm-Suspension on the Eggs 



OF THE .S.\ME INDIVIDUAL. 



As soon as it was found tiiat Cimut intentiixtli/y at Naples is not 

 totally self-sterile, but is self-fertile to a very varying degree in different 

 individuals, the proposed heredity experiments referred to in the 

 introduction had to be postponed until the limits and conditions of 

 self-fertility had been settled. In the preceding sections some of the 

 main factors have been described which influence the degree of self- 

 fertility, and although the latter is very variable, it has been shown that 

 a very much greater concentration of sperm is always necessary to 

 bring it about than is required to effect cross-fertilization. Moreover a 

 considerable proportion of individuals are always present, the eggs of 

 which cannot be self-fertilized at all. 



The causes of this self-sterility have been investigated before, but 

 although the problem has been narrowed down considerably, they 

 remain fundamentally as obscure as ever. It was with a view to 



