322 T. H. MORGAN. 



The converse experiment should also be carried out at the 

 same time ; namely, that in which the sperm of A is put into 

 the extract of B in order to see if it might not be made active so 

 that it would then fertilize its own eggs. In my previous paper 

 I have described some experiments of this kind. As a check to 

 this the a-sperm should be put into the B-extract and then later 

 the B-eggs added to show whether the extract itself may not 

 interfere with the fertilization. The complete experiment is 

 indicated in the following table : 



A-sperm. 

 B-sperm. 



Experiment I. - -In one experiment in which an extract of the 

 ovary of the individuals was used none of the eggs segmented 

 showing that even the extract of another individual prevents the 

 cross-fertilization from taking place. A test experiment with 

 these same eggs and sperm, brought together in sea water, showed 

 that A-eggs with B-sperm gave only 20 per cent, of cases of seg- 

 mentation, and B-eggs with A-sperm gave no cases of fertiliza- 

 tion. It is clear, therefore, that the eggs and sperm were not in 

 very good condition. When self-fertilized in sea-water neither 

 the A-eggs or the B-eggs segmented. 



Experiment 2. In another experiment the eggs* and the ovary 

 of one individual (A] were soaked in sea water for one hour. 

 The same was done with the eggs and the ovary of another indi- 

 vidual (B). The sperm of A was added to the A- extract and 

 the B-sperm to the B-extract for half an hour. Then the B-eggs 

 were placed with the A-sperm that had been in the A-extract, 

 and the A-eggs with the B-extract and B-sperm. None of the 

 eggs divided. In this same experiment the B-sperm was put 

 into the extract of the ovary of A, and later the A-eggs were 

 added ; similarly for the A-sperm. No eggs were cross-fertil- 

 ized, showing as in the preceding case that the extract itself had 

 interfered with cross-fertilization (provided the eggs were good 

 which was not tested). 



