314 T. H. MORGAN. 



this result would follow, provided the substance that prevents 

 self-fertilization is soluble in sea water. This experiment I have 

 carried out during the past summer in a variety of ways, but have 

 found that the anticipated results did not follow, from which I am 

 led to conclude that the phenomenon is not due to a substance 

 that is soluble. 



The failure of this experiment to give positive results showed 

 me that I must start once more at the very beginning, and test 

 more thoroughly the assumption that the sperm of one individual, 

 if in good condition, is capable of fertilizing equally well the eggs 

 of all other individuals ; for the difficulty of explaining the re- 

 sults becomes immensely greater if this condition holds abso- 

 lutely. If it does hold it would mean that the conditions present 

 in an individual are not found in any degree in any other indi- 

 vidual. The principal results of this paper deal, therefore, mainly 

 with this question, although, at the same time, I have described 

 some other experiments which gave negative results, because, I 

 think, the results, negative though they be, will be of value in 

 determining the direction of further experiments. 



My work was carried out at the marine laboratory of the Uni- 

 versity of California, situated at present at Coronado Beach, Cal- 

 ifornia. I am under many obligations to the university for the 

 privilege of working at the station, and especially to the director, 

 Professor William E. Ritter, and to the resident naturalist, Mr. 

 B. M. Davis. It gives me great pleasure to acknowledge my appre- 

 ciation of the many courtesies extended to me during my sojourn 

 at the station. Professor Ritter informs me that the species of 

 dona at Coronado Beach appears to be identical with dona in- 

 testinalis of Europe. 



EXPERIMENTS IN CROSS-FERTILIZATION. 



The eggs of an individual were removed and distributed in six 

 dishes, A-A. Similarly the eggs of another individual were 

 taken out and distributed in six dishes, B B ; and, so on, for 

 four other individuals. See Table I. The sperm of A was then 

 removed from the vas deferens and added to A, B, C, D, E, F. 

 In the table the sperm is indicated by the small letters, a-f, 

 used as exponents. The sperm from each of the other five indi- 

 viduals was used in the same way. Thus all the eggs were 



