SEARS CROWELL 



307 



HYDRANTH DIFFERENTIATION^' 



The manner of development of thecate hydranths, their failure 

 to grow, and the fact that they regress after only about a week sug- 

 gest that they have little regenerative or regulative ability. We have 

 cut tentacles from young hydranths and find that they do not 

 regenerate appreciably. If the hypostome is cut off regression en- 

 sues within a few hours. To carry this matter further back into 

 stages of hydranth development we undertook several types of sim- 

 ple operations on hydranth buds. 



Athecate hydranths which have had parts removed replace 

 them. The three sketches of Figure 9, for example, illustrate the 



-T-rrrfi-^-TTr 



Fig. 9. Rapid restoration of tentacles and hypostome in Cordylophora 

 following the removal of the hypostome and most of the tentacles. 



^The experiments described in this section have not been presented elsewhere except 

 in abstracts (5, 6 ) . 



