DIFFERENTIAL DEVELOPMENTAL MODIFICATION. I 171 



inhibiting agents. Stages like Figure 59, B and C, may undergo regression 

 to forms essentially like F, G, and H and develop again if returned to 



Fig. 59, /1-L.— Normal and differentially inhibited development of hydroid of Corytnorpha 

 palma from planula. A-C, stages of normal development; D, E, differentially inhibited de- 

 velopment in planula stage; F, G, H, later stages of differentially inhibited development; /, /, 

 more extreme inhibition; K, L, regression from stage of B to planula-like stage. 



water. Regression of stages like Figure 59, B, to forms resembling early 

 planulae completely inclosed in perisarc is possible with inhibiting agents, 



