326 T. H. MORGAN. 



then to self-fertilize the egg-fragments, etc. Many of the eggs 

 that had been broken were self-fertilized, indicating that the re- 

 sistance to self-fertilization is due to something in the membranes 

 surrounding the eggs. The experiments need to be repeated on 

 a larger scale, but even if placed beyond doubt, the explanation 

 of what there is in the membranes that prevents self-fertilization 

 remains still to be determined. 



EXTRACT OF THE SPERM. 



Experiment 13. - - Wishing to see if an extract of the sperm 

 of one individual would cause the sperm of another individual to 

 fertilize its own eggs, the following experiment was made. The 

 sperm of three individuals was dried in the sun on a piece of 

 glass ; the residue, including the salt, was scratched off, and as 

 much tap water was added as there had been sea water before. 

 Sperm and eggs of another individual were then added to the 

 solution, but no results followed. 



DILUTING THE WATER. 



Experiment /./. In order to determine whether dilution of 

 the sea water might not bring about self-fertilization, the follow- 

 ing experiment was made : One, two, three, four or five parts of 

 tap water were added respectively to one hundred parts of sea 

 water. In all of these solutions cross fertilizations took place, 

 but in no case did self-fertilization occur. 



Experiment 75. - - In this case the eggs were first crossed and 

 then put into sea water, diluted as follows : 40, 50, 60, 70 parts 

 of tap water were added to 100 parts each of sea water. In the 

 first and second solutions about half of the eggs segmented into 

 several cells ; in the third solution few eggs segmented, and none 

 in the fourth, although they became polynuclear. The eggs of 

 three individuals were put, with their own sperm, into the same 

 solutions, but gave no results. 



SUMMARY. 



1. It is not true that the sperm of a given individual will fer- 

 tilize equally well the eggs of all other individuals. 



2. The eggs appear to be in good condition much oftenerthan 

 the sperm, but even good eggs cannot be fertilized equally well 

 by good sperm of all other individuals. 



