LAEVAL DEVELOPMENT IN THE SEA URCHIN 89 



by the differential action of the inhibiting agent, and that recov- 

 ery does not completely restore the usual metabolic relations 

 along the axes; consequently the metabolic differences are less 

 effective in determining localization and differentiation than in 

 the normal animal, or they are effective only in the apical region, 

 where recovery is most rapid. It is evident that energy for 

 development is available, for, in general, the greater the degree 

 of inhibition of development, the longer the life after recovery 

 before the animals die of starvation. It is not then that energy, 

 but rather that the pattern or plan of energy distribution which 

 the axial metabolic gradients afford is altered or more or less 

 completely obliterated. 



FORMS RESULTING FROM DIFFERENTIAL INHIBITION WITH GEN- 

 ERAL RECOVERY 



Where the degree of inhibition is so great, the effect so per- 

 sistent, or the period of inhibition so late in development that 

 differential recovery does not completely compensate or over- 

 compensate the morphological effects of inhibition, the general 

 recovery which follows return to seawater often serves to bring 

 out the differential effect of inhibition on the form and propor- 

 tions of the larva more clearly than does continued action of the 

 inhibiting agent. This is simply because development always 

 advances somewhat farther after the animals are returned to 

 water, and so the differential inhibitions may be carried to later 

 stages, than in the presence of the inhibiting agent. 



High concentrations of KCN, acting for a sufficiently long 

 period at or before the gastrula stage, give particularly interest- 

 ing results in this respect, because the inhibiting effect of high 

 concentrations of KCN is relatively persistent and is therefore 

 less completely compensated by differential recovery, but there 

 is no doubt that similar results can be obtained with NH 4 OH 

 and NaOH, and even with acids, if the degree of inhibition be 

 sufficient and the period of inhibition late enough in develop- 

 ment to prevent the occurrence of differential recovery before 

 the axial relations are fixed. 



