256 W. J. Ceozier, 



connected with ganglia at the ends of branches from the tentacle 

 or radial nerve strands; sensory cells of presumably similar function 

 also occur scattered over the body of synaptids, and in the general 

 eT^ithelmm. of Molapdiidae (Clark, 1907, p. 154). Claek suggests that 

 the cloacal papillae of the Molapdiidae, like the tentacle digits in 

 this and other Apodous groups, are important organs of touch. 

 Cucumaria and Holothuria have no special form of nerve termination 

 even in the tentacles (Cuénot 1891, p. 515; Retzius 1906), but the 

 podia and tentacles are each provided with an extension of the 

 nearest radial or tentacular nerve strand ending in a plate of 

 sensory epethelium at their distal terminations. Polaea (1906 b), 

 however, has found what may be (?) tactile organs, in the integument 

 of H. tuhulosa and H. poli. 



Henei (1903a, b, c) describes reactions of Stichopus regdlis which 

 point to the existence of ramifications of the radial "nerves", each 

 point on a longitudinal muscle being reflexly connected with a 

 series of points on the body which he finds located within a certain 

 limited region. He accounts for the different reactions obtained 

 from the anterior end near the mouth, by saying that here the 

 nerve-ring apparatus enters, and through its action as a conductor 

 a pair or more of the longitudinal muscles contract. He concludes 

 that the nerve ring acts as a central nervous organ. I have in- 

 cidentally verified some of Henei's observations on the mechanical 

 stimulation of the body-wall of SticJwpus {S. moeUi) cut open along 

 an inter-radius. The mode of reaction of the mid body wall of 

 Holothuria to tactile, photic (p. 261) and chemical (p. 67) stimuli, 

 leads me to believe that the nervous system oi Holothuria works in 

 a manner agreeing with Henei's description. But it must be noted, 

 on the other hand, that animals from which the "central nervous 

 organ" had been removed were still capable of coordinated activity, 

 — of moving away from the light, climbing vertical walls, and 

 turning the anterior end away from the side stimulated, — though 

 they appeared to be in a much weakened condition. Cole (1913b) 

 believes that a starfish with its circumoral nerve ring cut cannot 

 effect coordinated righting movements, but experiments shortly to 

 be described show that this is entirely possible for Holothuria, and 

 I therefore do not believe that the nerve ring necessarily acts as 

 a true central nervous organ in Henei's sense. 



Furthermore, the posterior end of Holothuria exhibits these 



