PHYSIOLOGY OF THE SPERMATOZOOxN 



III 



a) Activity ejfects. — The spermatozoa of some ani- 

 mals, e.g., Nereis and Arbacia, are normally active in 

 sea-water, and the specific egg water causes no noticeable 

 acceleration of their rate of movement under optimum 

 conditions. Others again are very inactive, but may be 

 aroused to intense activity by the specific egg water or 

 egg extract. This is true of the spermatozoa of Asterias, 

 for instance, during the summer season at Woods Hole. 

 But an activating substance is probably present even in 

 the case of species like Arbacia. Loeb points out that 

 the spermatozoa of both sea urchins and starfish are 

 immobile in a neutral n/2 NaCl solution in which they 

 will continue to live for days, but the addition of specific 

 eggs will in each case cause immediate and often intense 

 activity. There is a certain amount of specificity in 

 these eft'ects, as is shown by the following table, taken 

 from Loeb (1915): 



Specificity of xA.ctivation of Sperm by Eggs 



Thus the two kinds of starfish spermatozoa seem to 

 exhibit considerable specificity in their activation, 



