356 GRACE MEDES 



may be productive of a size greater than the normal is necessarily 

 the optimum for development. 



Just as increased growth is not necessarily correlated with 

 accelerated development, so decreased size need not be associ- 

 ated with abnormality of structure. In the solutions of Experi- 

 ment 3 in which a size above the normal is attained, there are 

 discernible some effects of previous adverse conditions. An 

 example of this is given in figure 32, which represents a speci- 

 men from solution d, Experiment 3, 96 hours. Although this 

 individual, — one of the extreme variants in the solution, at- 

 tained a size of 103, and its measurements taken on the two 

 sides would indicate a perfect symmetry, slight irregularities, 

 such as the presence of an accessory rod at the base of the 

 right arm and a bowing of the left body-rod suggest some ab- 

 normalities of development. This skeleton, moreover, lacks the 

 distinctive marks of those associated with growth in dilute solu- 

 tions, that is, general simplicity of structure. The spines are 

 about as numerous as under normal conditions, the ventral 

 body-branches are possibly even more highly- developed and the 

 point of fusion of the transverse rods is somewhat prominent. 

 All these suggest some influence of the concentrated condition 

 of the solution and suggest that a change of medium, even 

 when the larva is approaching its maximum size, may pro- 

 duce some effect upon the skeleton. 



Vernon ('95) gives a graph (fig. 5, loc. cit.) of the effect of 

 salinity on growth of Strongylocentrotus. He found ''that the 

 larvae reached their maximum growth in a solution containing 

 50 cub. centims. of distilled water per liter, where they are 15.6 

 per cent larger than those developed in water of normal condi- 

 tion. With greater dilution than this they steadily decrease in 

 size again, till in a solution containing 150 cub. centims. of dis- 

 tilled water per liter, they are on an average 4.3 per cent smaller 



than the normal When the sol. contains only 25 



cub. centims. of distilled water per liter, the larvae are 9.5 

 per cent larger than the normal, and when only 12.5 cub. 

 centims., 5 per cent larger." 



