DIFFERENTIAL DEVELOPMENTAL MODIFICATION. II 199 



DIFFERENTIAL INHIBITION 



In slight degrees of differential inhibition at early stages the oral lobe 

 is most inhibited, the angle between the anal arms (brachial angle) is 

 slightly decreased, and the foregut or esophagus is usually small (Fig. 73, 

 H, I); that is, apical and mid-ventral ectodermal regions are most in- 



D 



Fig. 74, ^-/^.—Differential inhibition in Arbacia. A-E, KCN; F-H, CUSO4 and LiCl 

 (A-E from Child, i9i6<^). 



hibited. With greater inhibition there is further reduction of the oral 

 lobe, often to complete absence, and further decrease of brachial angle to 

 parallel, fused, or single median arms with skeletal rods parallel or even 

 converging toward the tips (Fig. 74). In Figure 74, A-E are cyanide 

 material, F-H, CUSO4 and LiCl, with return to water after exposure long 

 enough so that the differential inhibition persists, although development 

 may continue. With such procedure the differential inhibition has become 



