LARVAE OF ARBACIA PUNCTULATA 351 



In 72 hours, solution c had become concentrated to about 

 the same specific gravity as that of a. We have then, at this 

 stage two solutions of almost identical concentration, one of 

 which has been maintained constantly in this condition and the 

 other of which has reached it through a process of gradual 

 evaporation; yet in the latter, the size, notwithstanding an 

 early inhibition, has increased materially above the normal. 

 As the concentration increases beyond that of sea-water, rate 

 of growth decreases, and at the age of 120 hours the plutei 

 are 0.5 per cent smaller than the control. We have therefore, 

 at this point, two solutions of different concentration, — the 

 one, that of normal sea-water with a specific gravity of 1.0223, 

 and the other, that of a concentrated solution of a specific 

 gravity of 1.0251, an increase of 12 per cent, in which the 

 larvae, by widely different courses of treatment, have reached 

 the same end. The ultimate effect could, of course, only be 

 speculated upon, but at this point two facts are evident; — first, 

 that we have in two similar solutions individuals of the same 

 parentage, reaching entirely, different conditions through unlike 

 treatment; and second, we have the same individuals, through 

 further dissimilar treatment, converging to the same point. 



In all these cultures of Experiment 3 the specimens were 

 the offspring of the same parents, but were subjected to such 

 widely different conditions that there was produced an increas- 

 ingly great primary inhibition of growth in the solutions from 

 a to g. Those in which this early inhibition was least marked, 

 i.e., those of the least dilution, are exposed at the close of the 

 experiment to the most unfavorable conditions. To what, 

 then, is this early inhibition due? To what extent may early 

 inhibition be overcome by later favorable conditions? In how 

 far may favorable conditions during the first hours of cleavage 

 so benefit the organism that later adverse circumstances fail 

 to produce modification of normal growth? And is an increased 

 size at any one period necessarily indicative of or coincident 

 with acceleration of development? 



The primary inhibition could be ascribed to either of two 

 causes, — first, shock attendant upon sudden change of medium 



