H. M. FucHS 255 



Reseda self-fertility is a Mendelian dominant to self-sterility. For 

 Clona, however, in those individuals where self-fertilization can most 

 easily be brought about, it takes place to a very much lesser degree 

 than does cross-fertilization. A much greater concentration of sperm is 

 needed to induce a comparatively high percentage of self-fertilized eggs 

 than would easily cross-fertilize all the eggs of another individual. On 

 the other hand many individuals were experimented upon at Naples in 

 which no eggs at all could be fertilized with sperm from the same 

 animal, although in general the Naples Ciona seems to be much more 

 self-fertile than the races used by Morgan. Again, in Reseda apparently 

 an individual is either self-fertile or self- sterile. This is not at all the 

 case with Ciona at Naples, where a given animal may vary widely in 

 its capacity for self-fertilization with each lot of eggs and sperm 

 produced'. 



The question arises as to whether the sterility of hermaphrodite 

 animals is confined to the genital products of the same individual; 

 whether all individuals are equally fertile when crossed with one another, 

 presupposing of course that the eggs and sperm are mature and in good 

 condition. Morgan attempted to investigate this question in Ciona and 

 concluded that all individuals are not equally fertile inter se. A discus- 

 sion of Morgan's methods has already been given (Section II) and it is 

 considered that his conclusions are unjustified. The question is not an 

 easy one to attack owing to the difficulty of making different sj^erm- 

 suspensions of nearly equal concentrations ; for a small difference in the 

 strength of a sperm-suspension makes a large difference in the pr(_)- 

 portion of eggs cross-fertilized. Nevertheless if there be considerable 

 variations in the degree of cross-fertility, variations at all comparable 

 with the extent of self-sterility, they would certainly be detected. It 

 was not attempted to investigate the question in the present work, but 

 it can be stated that in practically every case 100°/^ of segmenting eggs 

 could be obtained as a result of cross-fertilization, provided that enough 

 sperm was used. There were of course a few cases in which some of 

 the eggs were obviously pathological and could therefore not be fer- 

 tilized, but this does not affect the question. It is possible that the 

 degree of cross-fertility may be much less in nearly related individuals 

 (cf. Correns (4)), but this naturally cannot be decided with material 

 taken from the sea. It is hoped that the laboratory cultures now being 

 reared will shed further light on the subject. 



' This may have been somethhig like the same phenomeuou ia Correus' Cardaiiiiite, 

 for repeated poUmatious with the same plant did not alv^ays give the same result. 



