420 Harry Beat Torrey. 



only is the cauline coenosarc in Campanularian hydroids, e. g., 

 Obelia, fastened to the perisarcal tube here and there by multi- 

 cellular amoeboid processes of the ectoderm, but the anterior ends 

 of growing stolons exhibit amoeboid changes of form which ac- 

 count for their creeping movements and produce the tension often 

 manifested in the coenosarc which is fixed farther back on the 

 stem. The coenosarc is literally dragged out of the perisarc. 

 A similar tension has already been noted in the filaments of the 

 hold-fast, due to a similar cause. And it is probable that the 

 proximal end of the larva may be dragged along at times after the 

 more distal attached portion. 



The active muscular movements discussed at length for the 

 adult need not be considered here, as the young hydroid appears 

 to respond similarly in all respects, with the one exception that the 

 reaction times are somewhat greater. 



The absence of a free-swimming larval form seems to account 

 for the tendency of Corymorpha palma to dwell in communities, 

 as previously mentioned. The power of locomotion is too slight 

 to have any effect on the distribution of individuals, which is 

 accomplished by tidal currents and the shifting of surface sands. 

 Occasionally an individual may be washed away from its anchor- 

 age, and begin a new community in a new locality. 



SUMMARY. 



Corymorpha is unusually active for a hydroid. It is every- 

 where sensitive to mechanical stimuli, irritating chemicals and 

 abrupt changes in temperature, nowhere to "odorous" substances. 

 The prehensile mechanism is composed of proximal tentacles, 

 which move toward the mouth in response to all eff'ective stimuli; 

 distal tentacles, which move away from the mouth in their initial 

 response to stimuli; and proboscis, which may move toward the 

 point stimulated. These movements, as well as shortening and 

 possibly lengthening the stem, are performed by muscles. 



The stem of the adult responds to the stimulus of gravity, by 

 means of a change in the turgidity of the vacuolated axial cells. 

 The response of these cells varies according as the stem is attached 



