254 W- J- Ceozieb, 



had been made hypersensitive by chemical stimulation immediately 

 before the test, for example, as, by three or four applications of 

 M/50 acid.^) The body wall might be forced in over an area of about 

 a square centimeter by a v^ater current from a pipette without 

 producing any reaction. On severe prodding a rather complicated 

 series of reflexes was produced: a ring-like depression, deepest at 

 the point stimulated and usually disappearing on the ventral surface,, 

 was accompanied by a reaction from the anterior end such as I 

 have previously described under the responses to pinching a papilla. 

 Individuals resting on the bottom of an aquarium with a curve or 

 bend in the long axis were studied, and it was found that whether 

 the stimulus was applied on the inside or outside of the curve, — 

 i. e. to either the more contracted or the stretched side, — the- 

 bending away of the anterior end was such as to carry this part 

 away from the side stimulated.^) An exception to this general 

 statement was found in a somewhat different form of reaction,. 

 in which the pedicels, when stimulated in the manner above- 

 described, released their hold and the animal rolled over on 

 to the side opposite that stimulated; if stimulated again, as they 

 lay on one side, the bending of the anterior and posterior ends^ 

 was such as to bring them towards the spot touched. The latter 

 type of reflex depends upon the fact that the ventral musculature 

 is much more effective in producing body curvature than the dorsaL 

 The ventral and dorsal surfaces were of very nearly the same sen- 

 sitivity. The region in the immediate neighborhood of the cloaca, 

 behaved in a manner similar to that about the mouth, a slight touch 

 leading to the closure; of the cloaca, longitudinal contraction, and 

 some turning to the unstimulated side. Eeaction time (at 25") 

 averaged 0,6 seconds. 



When picked up and handled, or otherwise subjected to repeated 

 mechanical stimulation, Holothuria decreased markedly in volume. 

 Strong contraction of the longitudinal musculature forced out through 

 the cloaca water previously held in the respiratory trees, producing- 

 a decrease in length to little more than half its value in expansion^ 

 with only a slight increase in the maximum diameter (Table II), In 

 this process the pedate surface remained flattened, while the dorsal 



1) Jennings (1907, p. 69) found a similar interrelation between 

 mechanical and chemical stimuli in the staz'fish. 



2) This bending away of the anterior end involved, of course, the 

 release of the pedicels in that region. 



