1. It is not true that the sperm of a given individual will fertilize equally well the eggs of all other individuals. 2. The eggs appear to be in good condition much oftener than the sperm, but even good eggs cannot be fertilized equally well by good sperm of all other individuals. 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 crossfertilization 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 perfectly 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 fertilized 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 individual 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-fertilization, but the results are probably due to contamination. 12. Extracts of the sperm of other individuals did not, in the few cases tried, induce self-fertilization. 13. Dilution of the sea water does not facilitate self-fertilization, although cross-fertilization may still occur in water considerably diluted. 14. Eggs after standing for 24 hours in sea water are not fertilized by their own sperm. 15. Bursting the eggs, so that the membrane is ruptured or the egg is set free, allows self-fertilization to occur in a large number of cases, showing that the lack of self-fertilization of the unbroken egg is probably due to a resistance found in the surface of the egg, in the membrane, in the follicle cells or in their secretions.