Sensory reactions of Holothuria surinamensis. 



255 



surface became stronglj^ arched and the two ends much narrowed. 

 The relatively greater strength of the trivium muscles was shown 

 also in the way in which holothurians detatched from the substratum 

 and lying on one side became curved dorsoventrally, the ventral 

 surface occupjàng the inner curvature. Exactly opposite conditions 

 hold with Caudina, Thyone, and other forms (Geeould, 1896 ; Pearse, 

 1908, et al.), where the dorsal muscles become more powerfully con- 

 tracted when the animal is not attached to a horizontal base. 



Table II. 

 Showing relative sizes of holothurians expanded and in contraction. 





Normal 



Contracted 



No. 



length 



diameter 



length 



diameter 





cms 



cms 



cms 



cms 



1 



15.5 



2,0 



10,0 



2,5 



2 



10,0 



1,4 



4,0 



2,1 



3 



16.5 



2,1 



8,9 



3,2 



4 



19,1 



1,9 



9,0 



2,2 



5 



18,0 



1,8 



8.6 



2,5 



d) Experiments on mutilated animals. Small isolated 

 anterior and posterior ends, and the two parts of bisected animals, 

 reacted normally to tactile stimuli, except in the immediate neigh- 

 borhood of the cut surface. The responses of tube feet and tentacles 

 on isolated parts were of very slight amplitude, as compared with 

 those of the normal animal, but otherwise no differences could be 

 detected. 



e) Discussion. The reactions of E. surinamensis to tactile 

 stimuli may be summarized as follows: 



AU parts of the body are sensitive to touch, the order of respon- 

 siveness being tentacles, oral brim >• cloacal brim > podia >> anterior 

 end > posterior end >> mid-body surface. As in many other animals, 

 the anterior and posterior ends as a whole are the most sensitive 

 regions, and the anterior one is the more reactive. The tentacles 

 and podia (including the cloacal papillae) are the chief organs of the 

 tactile sense. 



The end-organs concerned in the reception of tactile stimuli 

 cannot be specifically designated. In synaptids (Clark, 1907, p. 47) 

 the so-called touch papillae are small groups of epithelial cells 



