Sensory reactions of Holothuria surinamensis. 243 



Expt. 33,1. 



July 3. 4,05 P.M. Three animals had nerve ring, etc., removed. 



5,15 P.M. Tube feet expanded, and waving about in normal fashion. 



9,00 P.M. "Decapitated" pieces gave a well-defined orienting reaction 

 to light from an oil lamp, moving away from the light (see page 261) 

 anterior end foremost. Quickly exhausted after 10 minutes stimulation. 



The phenomena of locomotion in Holothuria point to the existence 

 in this animal of a strongly developed physiological polarity, anal- 

 ogous to that seen more vaguely in Asterias and in spatangoids. 

 The reason why this polarity is not so clear in TJiyone is to be 

 found, I believe, in the fact that this form bears tube-feet scattered 

 over its whole surface, whereas those of Holothuria are strictly con- 

 fined to its "ventral" side, or trivium. 



f) Auto-evisceration, The curious habit of casting out 

 the viscera in response to intense irritation, or when the conditions 

 of existence have become particularly unfavorable, has long been 

 remarked in holothurians (Daltell, 1851, and many later workers). 

 It is not confined to this group, but is exhibited also by crinoids 

 [Antedon] Dendy, 1886) and starfishes {Cribrella; Colg-an, 1912). 

 Peakse (1909) studied visceral autotomy in TJiyone with special re- 

 ference to the rôle played by the nervous system. In agreement 

 with the views of Cuénot (1891) and of Claek (1901j, he regarded 

 autotomy as a result of pathological conditions, probably operating 

 through a reflex system of the sort known to exsist among 

 arthropods. There would seem to be several distinct grades of 

 autotomy practiced by holothurians : Synapta (Peaese, 1909) pinches 

 off fragments from the posterior end, and the reaction depends on 

 the presence, of the nerve ring; Thyone (Peakse, 1909) ejects the 

 vicera through a rupture in the body- wall near the calcareous ring; 

 holothurians possessing Cuvierian organs cast them out through the 

 cloaca, and may or may not accompany them with more or less of 

 the intestine, depending on the species and the exciting circum- 

 stances. To these categories of autotomy must be added the pro- 

 cess of self-division (Dalyell, 1851, see also p. 246) employed (?) as 

 a method of reproduction. 



It was mentioned in the section or anatomy that H. surinamensis 

 has the Cuvierian organs poorly developed. The discharge of "cotton" 

 is therefore not a feature of the animal's behavior; but under certain 

 conditions the gut, respiratory trees, etc. were cast out through the 

 cloacal aperture, or even through the mouth (though this was un- 



