SELF-FERTILIZATION IN CIONA. 327 



3. In the case of poor sperm the discrimination shown between 

 the eggs of different individuals is apparently more marked than 

 in the case where the sperm is unusually good. 



4. The results are not due to different amounts of sperm used 

 in different cases, because the same, or nearly the same amount 

 was used in each series. Other experiments showed that the 

 amount of sperm used was many times greater than that sufficient 

 to fertilize all the eggs present. On the other hand by using a 

 larger amount of " poor " sperm the percentage of cases of cross- 

 fertilization could probably be increased. 



5. There is no definite relation between the number of eggs 

 that are cross-fertilized and the normal or abnormal condition of 

 the tadpoles. Previous experiments had also shown that per- 

 fectly normal tadpoles may be produced by self-fertilization in the 

 few cases in which this takes place naturally or is induced. 



6. If a strong extract of the ovary of an individual (A) is made, 

 and the sperm of A (first made active in sea water) is added, and 

 if then the eggs of B are also put in, they may not be fer- 

 tilized if the solution is very strong, but if it is diluted fertilization 

 may take place. Thus the A-sperm is not brought to rest by an 

 A-extract, except in so far as the solution is too strong to allow 

 any fertilization, as is shown when A-sperm is put into B-extract 

 and B-eggs added --no fertilization taking place in the strong 

 solution, but occurring if dilution is subsequently brought about. 



7. If A-sperm is put into an extract of the ovary of B, and then 

 A-eggs are added no fertilization occurs, showing that the extract 

 of another individual does not excite the sperm to self-fertilization. 



8. If the eggs of an individual (A) are placed in an extract of 

 the ovary of B, then returned to sea-water and A-sperm added, 

 self-fertilization does not occur. The extract of B does not effect 

 the A-egg so that they will self-fertilize. 



9. The blood and extracts of the body tissues of another in- 

 dividual give similar negative results. 



10. Shaking the eggs, so that the follicle cells are removed, 

 favors self-fertilization. 



11. Placing the eggs and sperm of one individual in the 

 " follicle-water " (obtained by shaking) of another individual 

 gave distinctly increasing percentages of apparent self-fertiliza- 

 tion, but the results are probably due to contamination. 



