424 GEACE MEDES 



In how far may these combined factors modify normal develop- 

 ment? In many of the experimental solutions in which condi- 

 tions are so adverse that life is barely maintained, the measure- 

 ments come well within the range of size of the controls. In the 

 first experiment with concentrated medium (2), the measure- 

 ments of the specimens subjected to 40 per cent concentration 

 (e +), which lived only 96 hours, are greater than those indi- 

 cated by IF (Plot 1) for the corresponding days, and drops be- 

 neath*those of IFF only at the 96 hour stage. The same is true 

 of the specimens in the solution of 30 per cent .dilution, which 

 lived only 96 hours, except that at the age of 72 hours they 

 measured slightly more than those in IF. 



These two solutions represent the limits to which concentra- 

 tion and dilution could be pushed, and yet the size of the larva 

 was not reduced below that of the extreme variants of the 

 control cultures. In the second experiment with NaHCOs (9), 

 the same conditions may be observed. In the culture with 91 

 cc. sea-water + 9 cc. 0.45 NaHCOs, the larvae were in a dying 

 condition at the close of the fourth day. At the ages of 24, 48 

 and 72 hours they were well within the range of the controls, 

 and at the age of 96 hours were within IF but below IFF. Like- 

 wise in the experiment with carbon dioxide (20(/), the same con- 

 ditions occur. Not until 96 hours, after 24 hours of almost 

 complete inhibition of growth, does the average measurement 

 drop below that of IFF. 



It is significant that these three experiments were performed 

 during the early period (B), — a fact which may account for the 

 high resistance of the individuals to the foreign solutions. But 

 in other experiments made during the same period, in which 

 the controls seemed equally vigorous, life was maintained at a 

 much lower level. For instance, in the experiment with gradual 

 concentration of the sea-water (3), the specimens in the 

 solution of 120 cc. sea-water concentrated to 100 (e +), the 

 larvae lived 120 hours and seemed fairly vigorous at the close; 

 but except at the 24 hour period, when skeletons were pres- 

 ent merely as spicules scarcely tri-radiate, the measurements 

 were never within the range of the controls. This leads to our 



