H. M. FucHS 293 



himself has shown that the latter also contams a poison for Echinoid 

 spermatozoa. 



The result of the experiment described last shows that the effect of 

 Asterias egg-secretions on the sperm of other species is no different 

 from that of the other forms experimented with. The presence of a 

 substance in the Asteroid eggs which is poisonous for Echinoid sperma- 

 tozoa is interesting in itself but it cannot be an example of the general 

 way in which eggs protect themselves against fertilization by sperm of 

 other species. For if this were so, the extract of Giona eggs would not 

 have an equally stimulating effect on the spermatozoa of such a widely 

 different form as Strong ijlocentrotus as has the egg-extract of the latter 

 species itself 



IX. Effects of the H-ion Concentration of the Water on 

 THE Fertilizing Power of Sperm. 



In the experiments to be described in the two following sections 

 comparisons were made between the fertilizing powers of sperm-sus- 

 pensions of Cionu of equal concentrations made up (1) in normal sea- 

 water, and (2) in sea-water of altered H-ion concentration. The 

 experiments were carried out on exactly the same lines as those already 

 described on the effects of egg-secretions on the sperm. It may be 

 stated at once that the results showed an increase in the fertilizing 

 power in the presence of a slight decrease in the H-ion concentration, 

 and a very marked inhibition for a small increase in the latter. 



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



In each of the two experiments, the results of which are shown in 

 Table XXXV, two drops of a sperm-suspension of Giona were added to 

 each of the two dishes containing (1) 100 cc. normal sea- water, (2) 100 cc. 

 alkaline sea-water. The latter was made up by the addition of 1 cc. 

 N/10 NaOH to 200 cc. sea- water. 10 cc. of each of the suspensions 

 (1) and (2) were then poured on to separate approximately equal 

 quantities of eggs ft'om another individual of Giona. 



TABLE XXXV. (30.1.3.) 



Normal water Alkaline water 



Exp. 1. A/b 9 



Exp. 2. C/d 24 



Thus in both cases the effect of the alkaline water was to increase 

 the fertilizing power of the sperm-suspension. 



