400 Harry Beal Torrey. 



(Nagel, '94) toward stimulated points on the sub-umbrella. 

 While the excitation may be transmitted by means of the nerves of 

 the tentacles and proboscis, certain facts indicate that the direct 

 pull of the tentacle on the base of the proboscis serves at least to 

 reinforce the impulse and aid in guiding the tentacles and pro- 

 boscis in the proper direction. For example, the proboscis never 

 bends until the stimulated tentacle contracts, although this con- 

 traction may be delayed half a second or a second after the 

 stimulus is applied — an unusual reaction time; it does bend, how- 

 ever, immediately upon the contraction of the tentacle. Again, 

 when a simple grip of the forceps does not cause a movement of 

 the proboscis, the movement may be induced by adding to the 

 tactual stimulus a definite tension stimulus by pulling the tentacle 

 or preventing it altogether from shortening. 



Not only may stimulation of a proximal tentacle be followed by 

 movements of distal tentacles and proboscis, but by movements 

 of the stem as well, which contracts strongly when the stimulation 

 is vigorous. Only that part of the stem ordinarily contracts 

 which is not invested with perisarc, though the latter is too thin to 

 be an effectual hindrance to contraction in the basal region, which 

 at times does shorten considerably. 



When one distal tentacle is pinched, the response is similar to 

 what occurs when the disal tentacles respond reflexly to a stimu- 

 lation of a proximal tentacle; that is, several or all the distal ten- 

 tacles may wave outward and downward together, or indiscrimi- 

 nately outward. In response to this stimulus, the movement is 

 always away from, never toward the mouth; in this respect it is 

 contrary to the direction of the movement of the proximal ten- 

 tacles. After the first reaction, however, the tentacles may move 

 actively and singly toward and away from the mouth. This is 

 the characteristic reaction when the stimulation is prolonged. 

 The presence of a large food organism in the proboscis cavity will 

 cause such movements, which will persist until it has been 

 entirely swallowed. They are only moderately efficient, for the 

 outward movement of each tentacle is quite as strong as the in- 

 ward movement, and the tentacle retains its hold on the captured 

 organism for an instant only. They are indeed far less efficient 



