2o8 PROBLEMS OF FERTILIZATION 



dishes of each were selfed and the second two of each 

 crossed with quantities of sperm shown. The results 

 are expressed as percentages of eggs segmenting. It 

 will be observed that the lesser quantity of sperm suf- 

 ficed in cross-fertilization to cause the segmentation of 

 every egg, but was without any effect in the case of three 

 of the four self-fertilizations, and fertilized only 12 per 

 cent in the case of the other ; the higher concentration of 

 sperm caused some self-fertilization in every case recorded 

 in the table, though it seems probable from other state- 

 ments that this is not always the case. Fuchs also 

 determined,, as I interpret his results, that staling of 

 the eggs in sea-water increases their susceptibility to 

 self-fertilization up to a certain point; this was in 

 marked contrast to cross-fertilization. Morgan has 

 attempted to bring about self-fertilization by the action 

 of ether, alcohol, chlorotone, and other substances, with 

 results that must in general be regarded as negative, 

 for they were often contradictory. 



There appears to be a certain general resemblance 

 between resistance to hybrid and to self-fertilization, 

 because the same conditions may overcome either; it 

 must, however, be admitted that the data on the self- 

 fertilization are rather scanty and inconsistent in this 

 particular. The evidence is, nevertheless, adequate to 

 prove that the resistance is cortical in the one case as 

 in the other, and that when this cortical resistance is 

 overcome the internal events of fertilization proceed 

 normally. 



Are the eggs of Ciona equally fertile to the sperm 

 of all other individuals, or is there a certain degree of 

 individual as well as of self-incompatibiHty ? In an 



