H. M. FiTCHs -287 



stood for a considerable time with a large volume of eggs, this egg- 

 water had an acid reaction, and it is not to be wondered at that this 

 acidity counteracted the stimulating effect of the egg-water on the 

 sperm, which latter is clearly shown in the other experiments (Tables 

 XXIV and XXYII)i. 



The end result of the experiments described in the preceding five 

 sections is therefore that treatment of the spermatozoa of Giona with 

 egg-extracts of Phallusia, Arbacia or Strong ylocentrotus or with the 

 egg-waters of the two latter, increases its fertilizing power. 



VIII. Further Experiments to test the Specificity of the 



Egg-secretions. 



The experiments described in the last sections seem to show that the 

 general specific capability of spermatozoa for fertilizing eggs of the same 

 species only is not due to their being unstimulated by the egg-secretions 

 of other species. There remains, however, one other possibility in this 

 connection. It might be that the specificity of fertilization phenomena 

 depends on the relatively greater excitation of the spermatozoa by 

 secretions of the eggs of the same species than by those of others. This 

 suggestion can be tried by making strict comparisons between the effects 

 on the fertilizing power of sperm -suspensions produced by extracts from 

 the eggs of the same and of other species. The hypothesis was 

 thoroughly tested in the experiments described below. 



1. Comparisons of the effects of Strongylocentrotus and of Ciona. 

 egg-extract on the fertilizing power of Strongylocentrotus sperm. 



The chief difficulty encountered in making these experiments is the 

 practical impossibility of making two different egg-extracts of exactly 

 equal concentrations. They were made as nearly as possible of the same 

 strength by taking approximately equal ([uantities of the eggs of the 

 two species to be experimented upon, crushing them to the same extent, 

 and then washing off the juices into exactly equal quantities of water. 

 Diffei-ences of one or two per cent, in the fertilization percentages of 

 eggs fertilized with sperms treated with two different extracts are 

 probably to be accounted for by slight differences in the concentrations 

 of the extracts. 



' It should be noted that all other experiments with egg-waters described in this paper 

 were made under the same conditions as those of Tables XXIV and XXVII, thus eliminating 

 the acidity factor. 



