LARVAE OF ARBACIA PUNCTULATA 383 



These experiments indicate that the effect of alkaHnity upon 

 rate of development is immediate, and decreases in intensity 

 during later stages. This later retardation of growth may be a 

 secondary effect produced as a result of the embryo's having 

 exceeded its optimum rate. In other words, there may be a 

 point beyond which rapid development ceases to be beneficial 

 to the organism and hence precocious growth may be conducive 

 to later inhibition. This fact is shown more clearly in the 

 case of the very alkaline solutions where overrapid development 

 leads at once to irregularity of structure and inhibition of 

 growth. 



The specific effect of the hydroxyl may be said, then, to be an 

 acceleration of the rate of growth in the early stages, succeeded 

 by inhibition. In very weak solutions both these effects are 

 slight, but the greater the alkalinity, the more rapid the accel- 

 eration and the more marked the succeeding asymmetry and 

 inhibition. The effect, of course, is not exactly proportional to 

 the amount of alkali added, since, in the higher concentrations, 

 some magnesium and calcium hydroxides must precipitate out. 



In the experiments given above (Experiment 6), the limit of 

 endurance was reached when 2 cc. N/10 NaOH were added to 

 98 cc. sea-water, but in an experiment of the following year, 

 the limit was found to be 3 cc. N 10 NaOH to 97 cc. sea-water. 

 The concentration productive of maximum rate of growth at 

 each stage was found to be about the same, the only material dif- 

 ference in the reaction of the embryos to the changed environ- 

 ment being a greater degree of resistance, characterized by a 

 more retarded setting in of the typical abnormalities. 



In the carbonate solutions we also have acceleration of de- 

 velopment by the alkalinity produced as a result of the hydrol- 

 ysis of NaHCOs and Na2C03, both salts of a strong base with 

 a weak acid. In the bicarbonate solutions, as we should ex- 

 pect, acceleration is slighter and in stronger solutions is over- 

 shadowed by the specific effect of the carbonate. In the sodium 

 carbonate, especially in the weaker solutions, a third element 

 enters, the specific effect of the sodium, a fact which may be 



