96 C. M. CHILD 



tions of interest, but not directly connected with the chief pur- 

 pose of the investigation. 



One variable factor in the results, viz., the individual dif- 

 ferences in susceptibility in different eggs of the same female and 

 of different females cannot be controlled in these experiments. 

 In consequence of these differences the differential effect of a 

 particular concentration and period of action of a particular 

 agent is different in degree in different individuals and in dif- 

 ferent lots of eggs. Since large numbers of individuals are 

 used in each experiment a certain range of variation in the re- 

 sulting forms appears, but this is not great enough to obscure 

 the general effects. Some of the characteristic data for the 

 different agents used follow. 



Potassium cyanide 



In the most extensive series of experiments KCN was used 

 as the inhibiting agent, both continuously during development 

 and for short periods. The forms produced show differential 

 inhibition of greater or less degree as the characteristic feature, 

 and the degree of differential acclimation or recovery is slight. 

 The differential effect of KCN on the axial gradients is very per- 

 sistent, and, even though general recovery may occur on return 

 to water, there is but little differential recovery during the 

 period of larval development. The following data will serve to 

 indicate the range of concentrations and periods of action. 



Eggs placed in KCN ra/50000 at first cleavage and kept in this 

 concentration continuously, develop slowly to the blastula stage 

 where in some lots of eggs 25 to 30 per cent die completely, apical 

 end first, while in 25 to 40 per cent death begins apically, but 

 more or less of the basal region remains alive. In other lots 

 practically all remain alive, at least basally, but in a larger or 

 smaller percentage more or less apical death occurs. The final 

 stages attained show all degrees of differential inhibition, but 

 only rarely the slightest indications of differential acclimation. 



Development from the first cleavage in KCN m/100000 gives 

 little or no partial or total death and the forms produced show in 

 most cases only slight differential inhibition like figure 6. In 



