90 C. M. CHILD 



Narrow angled plutei like figures 6 A and B, are very char- 

 acteristic results of this procedure, but more extreme altera- 

 tions of the relations of parts are also of frequent occurrence. 

 Figures 82 to 87 (A basal, B lateral aspect), show characteristic 

 cases. In all of these the apical region is more inhibited than 

 the basal, but the more complete development of skeleton and 

 arms brings out more clearly the modification of form than 

 where the inhibiting agent is present throughout development. 

 In figure 13, a case of differential inhibition with practically 

 parallel skeletal rods was shown. Figure 82 A, B shows the 

 type of pluteus produced where such a degree of inhibition is the 

 result of temporary action of a high concentration followed by 

 return to water. Here the longitudinal rods and arms are 

 parallel; i.e., the metabolic differences between anterior and 

 posterior regions have been obliterated to such an extent that 

 both are of the same width. In figure 83 A, B, a somewhat 

 different modification occurs in that the two anal arms are 

 fused to form a flat, tapering structure and the arm rods approach 

 each other anteriorly, while the posterior portions of the skele- 

 ton still show some divergence. Figure 84 is another case of 

 fused arms, but with parallel posterior skeletal rods, figure 85 

 A, B, shows a still more complete fusion of the arms and figures 

 86 A, B, and 87 A, B, cases in which the skeleton is median in 

 position. In figure 86 the rectal region and anus are absent, 

 and in figure 87 the entoderm evidently has lost connection with 

 the blastopore region, but is fully differentiated, and the rectal 

 region is in contact with the posterior body wall, though an 

 anal opening could not be found. 



These forms show the changes in position and relations of 

 parts resulting from the differential effects of inhibition on the 

 minor axes. With decreasing metabolic difference between an- 

 terior and posterior ends, the skeletal rods become more or less 

 nearly parallel, and, in the transverse direction, the inhibition 

 is evidently greatest in the median region, for the width of the 

 body decreases, and structures, normally lateral, approach the 

 median line and finally become median as the degree of inhibi- 

 tion of normally median parts increases. 



