426 GRACE MEDES 



which NaCl was added to the sea-water (18 and 19) the con- 

 trol of the "first was one characteristic of that period, and the 

 measurements on the various days are not unlike those of the 

 general average for A. In the second, all the values for the 

 control are lower and correspond to Curve FF (Plot 1). A com- 

 parison of the figures obtained for the experimental solutions 

 shows that each measurement in the second experiment is less 

 than the corresponding one in the first, and the specimens were 

 less vigorous. 



Even when the experimental solution tends to produce increase 

 of size, the injury is more intense when the control possesses a 

 low average. For example, in the NaOH solutions, (6d) 2 cc. 

 N/10 NaOH to 98 cc. sea- water represented the highest concen- 

 tration of OH that could be endured by the larvae, but the fol- 

 lowing summer, when the animals were very vigorous, in one in- 

 stance (Oa) 3 cc. N/10 NeX)H to 97 cc. sea-water was employed. 

 It follows, then, that although abnormal conditions are not 

 always productive of reduced size, a size below the normal is 

 usually indicative of reduced vigor. 



What, then, is normal development? We cannot say that the 

 specimens of greatest size are necessarily normal, since some 

 changes of the medium, such as dilution of the sea-water or 

 concentration of the iiydroxyl, produce increased growth but 

 lead to secondary inhibition. Nor can we say that those are 

 normal which have developed under standard conditions of the 

 medium, since sea-water is exceedingly complex and variable. 

 Moreover, we have seen that other factors, such as the season 

 at which the eggs are produced and the staleness of the sexual 

 products modify development, and that the eggs of different 

 parents do not respond in the same way to similar treatment, 

 nor do all the eggs of the same parent react identically. 



Normal development we can regard only as the modal develop- 

 ment, and the mode must vary according to the place and the 

 time; that is to say, the environment. If some sudden change in 

 the composition of the medium were to occur, the largest class to 

 respond in a specific way would be regarded as normal; but a 

 few extreme variants might perhaps be best fitted to the new 



