Biological Studies on Corymorpha. 401 



than the tenacious tentacles of anemones with their more definite 

 movements. 



When the proboscis is pinched at its base, it bends toward the 

 point of stimulation, the distal tentacles waving. A pinch at any 

 point, of a sufficient intensity, will induce characteristic move- 

 ments of the distal and proximal tentacles and a shortening of the 

 stem. If the stimulus is not too strong, only the proximal and 

 distal tentacles in the vicinity of the point of stimulation will react 

 simultaneously. 



A slight stimulation of the stem may produce characteristic 

 movements of both sets of tentacles. The effect is not related to 

 the position of the point stimulated; none of the parts reacting 

 appear to distinguish the direction from which the impulse comes. 

 The stem may also shorten, even to half its original length. The 

 shortening usually takes place in the distal naked portion. The 

 proximal third, however, which is covered with perisarc, may also 

 contract; the perisarc is very delicate and in no way interferes with 

 this or any other movement of the stem.^ 



Chemical Stimuli. Several substances were used: flesh in the 

 shape of pieces of the shore gastropods Littorina and Acmcea, and 

 boiled ham; clove oil, alcohol and acetic acid. In no case did the 

 meat juices have the slightest appreciable effect on the hydroid; 

 the same may be said of the clove oil. Only when touched by a 

 stream of strong alcohol or acetic acid from a pipette did tentacles 

 or column respond; the acid killed the former almost instantly. 

 This response is evidently of the tactile order — as when an 

 irritating fluid is poured on the hand. Substances which have 

 for our perception odors and flavors, appear to produce no 

 reactions.^ 



^The proportion of stem covered by perisarc is based on measurements of 

 expanded individuals, under normal conditions. When a hydroid has been standing 

 in the same water for a week or two, it usually becomes much attenuated, and the 

 part of the stem invested with perisarc then often appears longer than the distal 

 naked portion. Often the ratio of the covered to the naked portion of the stem may 

 become that of the larva (Fig. 5). 



^Loeb ('95) has already criticised the use of the words "olfactory" and "gusta- 

 tory" to describe the reactions to chemical stimuli of animals of whose consciousness 

 we are as ignorant as we are of the consciousness of the Coelenterata. 



