FERTILITY 217 



binations that he made. There can be httle doubt 

 that he has pointed out the direction in which a solu- 

 tion is to be found. 



There is a somewhat similar case in animals. In one 

 of the Ascidians, Ciona intestinalis, an hermaphrodite, 

 the sperm will not fertilize the eggs of the same indi- 

 vidual. But the sperm will fertilize eggs of other 

 individuals, and vice versa. Castle first found out this 

 fact, and I have studied it on a large scale. The 

 diagram (Fig. 105) gives an example of one such ex- 

 periment made recently by W. S. Adkins. 



Five individuals are here used. The eggs of one 

 individual, A, were placed in five dishes (horizontal 

 line) ; likewise those of B, C, D, E. The sperm of A, 

 designated by a (vertical lines) was used to fertilize 

 the eggs. A, B, C, D, E ; likewise the sperm h, c, d, e. 

 The self-fertilized sets form the diagonal line in the 

 diagram and show no fertilization. The other sets 

 show various degrees of success, as indicated by the 

 percentage figures. These results can best be under- 

 stood, I think, by means of the following hypoth- 

 esis. The failure to self-fertilize, which is the main 

 problem, would seem to be due to the similarity in the 

 hereditary factors carried by eggs and sperm ; but 

 in the sperm, at least, reduction division has taken 

 place prior to fertilization, and therefore unless each 

 animal was homozygous (which from the nature of the 

 case cannot be assumed possible) the failure to fertilize 

 cannot be due to homozygosity. But both sperm and 

 eggs have developed under the influence of the total 

 or duplex number of hereditary factors ; hence they 

 are alike, i.e. their protoplasmic substance has been 



