SELF-FERTILIZATION IN CIONA. 321 



12 and 24 drops of a solution containing the sperm was added 

 to equivalent numbers of eggs, and gave 90, 90, 90, IOO per 

 cent, of eggs fertilized. In another case 3, 6, 12 and 24 drops 

 gave 6, 50, 90, 90 per cent. In the latter case three drops 

 were not enough ; six not quite enough ; but 12 and 24 sufficed. 

 Now since in all the other experiments more than 24 drops 

 were used the outcome must depend in only a small degree 

 on the quantity of sperm, and the results represent, therefore, 

 approximately the proportion of eggs and sperm capable of 



uniting. 



The tables show that the sperm is generally "at fault," when 

 fertilization does not occur, the eggs being in nearly all cases 

 capable of fertilization when good sperm is used, although, as 

 pointed out, some striking exceptions occur. Thus poor sperm 

 will sometimes fertilize more eggs of one set than of another, but 

 the better the sperm the more eggs it will fertilize as a rule. 



It is clear from the tables that it is erroneous to suppose that 

 the sperm will fertilize equally the eggs of all other individuals. 

 All degrees of sterility are met with in cases where other experi- 

 ments with the same sperm fully succeed. Therefore the problem 

 is not so sharply defined as appeared to be the case before these 

 experiments were made. 



EXPERIMENTS TO DETERMINE THE NATURE OF THE INFLUENCES 

 PREVENTING SELF-FERTILIZATION. 



As stated above these experiments were undertaken in the 

 hope of finding out whether there is a soluble substance in the 

 eggs or body tissues of an individual that so affects its own sperm 

 that it is rendered incapable of fertilizing its own eggs. If this 

 is the case it would seem probable that the sperm might be 

 affected by extracts of its " own " tissues, so that it might no 

 longer be capable of cross-fertilization, if eggs of another indi- 

 vidual were added to the extract containing the sperm. 



The experiments to test this are not so simple as may appear 

 on first thought, since check experiments must be carried out in 

 order to see whether the same action may not result when 

 extracts of the body of another individual are used. In fact it 

 would have been very easy to make a serious blunder had not 

 this precaution been taken. 



