172 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



but renewed development of these forms following return to water has 

 not been observed. These regressions take place without visible disinte- 

 gration, but the tentacle cells are apparently resorbed and may serve as 

 nutrition. No evidence of specificity of the various modifications for any 

 agent used has been found, and comparison with the lethal susceptibilities 

 (pp. 10 1-4) and with results of differential dye reduction shows that 

 the same gradient pattern is indicated by the different methods.' 



Fig. 60, A-C. — Boiigainvillia mertensii. Stolon development from hydranth-stem axes 

 under inhibiting conditions. A, 48 hr. in ethyl urethane m/200; B, KCN m/50,000; C, KCN 

 m/50,000 for 6 days, then KCN m/ioo,ooo with further decrease in concentration for 8 days 

 (from Child, 1923a). 



The transformation of hydranth-stem axes into stolon axes in hydroids 

 is of interest as a differential inhibition in later stages of these forms 

 (Child, 1923a). From the study of many hydroid species it appears that 

 hydranths are much more susceptible than stolons and that the motile 

 hydranth is more susceptible than the nonmotile bud. In some hydroid 

 species stolons are not infrequently found developing from apical ends of 



' The data on Corymorplui have not been previously published. 



