308 HOMER W. SMITH AND G. II. A. CLOWES. 



longest time their capacity to fertilize (or to develop) in their 

 normal habitat, sea water, the H-ion concentration of which rarely 

 varies beyond pH 7.8 to 8.4. Contrarily, both Arbacia and 

 Asterias eggs retain their viability longest, and are least suscep- 

 tible to cytolysis, in quite acid solutions ; the optimum reaction for 

 Asterias lies between pH 6.2 and 6.6, and for Arbacia, 5.8 to 6.0. 

 The eggs of both species die with great rapidity in very alkaline 

 (pH 10.0) and very acid (pH 4.5) solutions; the rate of injury 

 appears to decrease uniformly as the optimum is approached, par- 

 ticularly from the alkaline side. There is no disproportionate 

 alteration in the rate of death around the pH of sea water. It will 

 be noted that the optimum does not occur midway between the 

 extremes but nearer the acid limits. That is, with respect to the 

 optimum, the eggs of both species can tolerate a larger increase in 

 alkalinity than in acidity. The Arbacia egg retains its fertilizing 

 capacity much longer at all H-ion concentrations than does the 

 Asterias egg. 



It is well known that batches of Asterias eggs are frequently 

 encountered in which all the eggs will not maturate or, even when 

 maturated, will not fertilize. Ralph Lillie (4) has shown that the 

 general physiological condition of such eggs could be greatly im- 

 proved by treatment with ether, as shown by an increase in the 

 number of eggs which both fertilize and divide. Similarly we 

 find that after a short exposure to slightly alkaline sea water 

 (pH 8.2 to 9.4), the proportion of fertilized eggs in these refrac- 

 tive lots is increased. This is expressed in Fig. 2 by the slightly 

 higher incidence of fertilization on the alkaline side of sea water. 

 This effect is clearly a more or less permanent alteration of the egg, 

 since the eggs were transferred from the alkaline solution to 

 normal sea water before insemination. It has sometimes been ob- 

 served that the proportion of fertilizable eggs is decreased by a 

 short exposure (3 to 5 minutes) to pH 10.0-10.2, and subse- 

 quently increased by longer exposures, short of permanent in- 

 jury. No reason can be given for this apparent transient injury. 



Goldfarb (5) has made careful studies of the consequences 

 of ageing in sea water of three species of sea urchin eggs. Ar- 

 bacia, Hipponoe and Toxopneustes. He finds that with increased 

 ageing there is an increased tendency for agglutination, fusion of 



