260 Studies in the Physiology of Fertilization 



PACE 



5. Comparison of the effects of Stron/iiilocenlrotus and EchimiK eg;,'- 



extracts on the fertilizing power of Strungylocentrotus sperm used 



to fertilize Echinus eggs 289 



6. Comparison of the effects of Strongrjloeentrntus and Asleria^ egg- 



extracts on the fertilizing power of Strongiilocentrolus sperm . 291 



7. Comparison of the effects of Strotipyloceiilroliif and Asterias egg- 



waters on the fertilizing power of Strongylocentrotus sperm . 292 



IX. Effects of the H-ion concentration of the water on the fertilizing power of 



sperm ............ 293 



1. Effect of a decrease in H-ion concentration ..... 293 



2. Effect of an increase in Hion concentration 294 



8. The reactions of Ciona and -■l-stcrins egg-extracts and of Cioiia blood 296 

 X. Conclusion 298 



XI. Summary of experimental results 300 



References 301 



I. Introduction. 



The investigations described in this paper arose out of experiments 

 on self-fertilization in Ciona intestinalis, an account of which is given in 

 the previous part of this paper. The present experiments were carried 

 out in part over the same period as those on self-fertilization, namely 

 during the spring and summer of 1913. The whole of the work was 

 done at the Zoological Station, Naples, and to the staff of this institution 

 I owe my very best thanks for the willing advice and help given to me 

 throughout my stay. 



The fact of self-sterility in Ciona, whether comparative or absolute, 

 suggested that some substance may be exuded by the eggs which 

 paralyzes the spermatozoa of the same individual, but does not affect 

 those of other individuals — or there might be something within the 

 egg envelope which acts in the same way. To test this hypothesis 

 experiments were commenced by trying the action of suspensions of 

 crushed eggs in sea-water on the spennatozoa. It was soon found that 

 there was a very large number of questions with regard to the action of 

 such egg-extracts on spermatozoa used to effect ordinary cross-fertiliza- 

 tion which must be investigated and cleared up before the more special 

 question of the mechanism of self-sterility could be attacked. The 

 outcome of these investigations with cross-fertilization is recorded in 

 this part of the paper. 



The results obtained are all based on numerical data. They 

 depend on the comparison of the proportions of eggs fertilized by sperm- 



