306 HOMER W. SMITH AND G. H. A. CLOWES. 



washed and gently agitated several times. Arbacia eggs were 

 washed with sea water twice after removal from the ovaries and 

 then used at once. The eggs were gathered into a concentrated 

 suspension by gently centrifuging and a few drops of this sus- 

 pension added to 200 cc. of the pH solutions contained in finger 

 bowls. A small quantity of eggs was used so that there would 

 be little crowding when the eggs settled to the bottoms of the 

 bowls. During the exposure they were frequently agitated. At 

 various intervals samples were transferred to .sea water and in- 

 seminated with fresh sperm. The samples were examined after 

 the eggs had had time to divide, noting both the number which 

 fertilized, as shown by the presence of a fertilization membrane, 

 and the number which had divided. 



The results of several experiments with each species have 

 shown that, as might be expected, there is some variation in the 

 behavior of eggs from different individuals. The extremely arti- 

 ficial method by which the eggs are obtained that is the excision 

 of the ovaries and the consequent forced shedding is not a 

 method which could be expected to give eggs of uniform physi- 

 ological quality from several individuals. But differences in the 

 actual time of survival of eggs from different individuals, though 

 important in some respects, do not materially alter the relative 

 time of survival at different H-ion concentrations. Since the 

 actual time of survival in any one experiment has no particular 

 significance, it has been thought best to omit the extensive tabular 

 data and to express the results in diagrammatic form with such 

 quantitative expression as can reasonably be implied. 



The relations between viability and H-ion concentration of 

 Arbacia and Asterias eggs are given in Figs. I and 2. In these 

 figures each contour line represents the proportion of eggs sur- 

 viving at a definite interval after transfer to the pH solutions, the 

 time of testing being marked on each curve. The data are based 

 on the average results obtained from several experiments. The 

 dotted curves marked " cytolyzed " show the proportion of cyto- 

 lyzed eggs at the conclusion of the experiments. The full ordinate 

 in these and all following diagrams indicates the H-ion concentra- 

 tion of sea water, i.e., pH 8.15. 



It might be supposed that marine eggs would retain for the 



