LARVAE OF ARBACIA PUNCTULATA ' 401 



b) Increase of alkalinity above the normal causes aceelera- 

 tion, accompanied by irregularity of form, and finally, inhibi- 

 tion. When this increase of alkalinity is slight, the resulting 

 injury is small, but with greater concentrations of the OH ion 

 the effect is correspondingly more pronounced. In very strong 

 solutions, varying from two to three cc. of N/10 NaOH per 100 

 cc. of sea-water, cleavage is irregular, and abnormal blastulae 

 are formed which fail to undergo gastrulation. 



c) Addition of carbonates produces a double effect: — 



1) Increase of OH concentration, by which the typical effect of 

 increased alkalinity upon rate of growth is brought about. 



2) Increased bulk of skeleton, due possibly to the fact that 

 the Mg and Ca carbonates are nearer to the point of saturation 

 in the modified medium. 



The following experiment was made for the purpose of deter- 

 mining the effects upon development of carbon dioxide, the 

 product of metabolism present in greatest proportions in the 

 sea-water. To what extent it could exert any influence upon 

 the young sea-urchins in their natural environment must be 

 largely a matter of conjecture, but some effect is to be inferred 

 from the fact that very minute amounts of acid produce marked 

 inhibition in development and decrease of size. 



A saturated solution of COo in sea-water was, prepared and, 

 for the various cultures, portions of this were diluted with 

 sea-water as tabulated below. The solutions were changed the 

 usual number of times until the blastulae began to swim, at 

 about six hours after fertilization, then three times daily. Each 

 time, they were prepared immediately before using, so as to main- 

 tain as nearly as possible a constant amount of CO2 in the medium. 

 The following concentrations were employed: 



Experiment 20. Plot 19. July 2, 1915 



a Sea-water 



h 99.5 cc. S. W. + 0.5 cc. S. W. saturated with CO2 



c 99.0 cc. S. W. + 1.0 cc. S. W. saturated with CO2 



d 98.5 cc. S. W. + 1.5 cc. S. W. saturated with CO. 



e 98.0 cc. S. W. + 2.0 cc. S. W. saturated with CO2 



/ 97.5 cc. S. W. + 2.5 cc. S. W. saturated with CO2 



g 97.0 cc. S. W. + 3.0 cc. S. W. saturated with CO2 



