SPECIFICITY IN FERTILIZATION 



207 



of self-fertilization when none exists. But Fuchs has 

 shown that shed spermatozoa will not survive over 

 twenty-four hours in sea- water, so that the tests arc 

 probably valid for determinations after twenty-four 

 hours of isolation, on the assumption that in the case 

 of pairs both individuals shed their gametes. Castle 

 himself suspects contamination in the two cases of appar- 

 ent self-fertilization yielding 90 per cent of fertilized eggs. 



To avoid this objection artificial insemination has 

 been practiced by the three authors named. In these 

 experiments Morgan finds an almost vanishing amount 

 of self-fertilization; while Fuchs working in Naples 

 found that, while in many cases no eggs segmented 

 after self-fertilization, nevertheless Ciona intestijialis as 

 a species is far from being completely self-sterile, though 

 ''a greater concentration of sperm is usually necessary 

 to bring about any self-fertilization than would cross- 

 fertihze 100 per cent of foreign eggs." 



May self-fertilization be forced on these eggs ? 

 Fuchs found that by increasing the quantit}' of sperm 

 a higher percentage of self-fertilization could be secured, 

 as shown in the following table: 



Equal amounts of eggs of four specimens were added 

 to four equal quantities of sea-water, and the first two 



