240 W. J. CßOZIER, 



that of the period of closure. That the mechanism concerned with 

 rhythmic movement of the cloaca is strictly local is shown by the 

 following experiment: 



Exp. 92,2. 



July 28. 5,00 P.M. Posterior ends 5 — 6 mm long removed from 

 five animals. 



9,00 P.M. Edges of wound turned in, but closure not complete. 

 Cloacal end was opening and closing rhythmically ; time for ten pulsations 

 = 1 min. 9 secs. 27^. 



July 29. 9,30 P.M. Rhythm of anal pieces continued; time for 

 ten pulsations = 1 min. 22 secs. 27,5^. 



The regular movement interrupted at about every seventh closure by 

 one of greater vigor and completeness, as in the intact animal. 



July 30. 2,30 P.M. Rhythmic movements continued, though less 

 vigorous; time for ten pulsations = 1 min. 50 secs. 27^. 

 Aug. 1. 9,00 A.M. Pieces dead and decomposing. 



Rhythmic movement of the cloaca was maintained for about 

 two days by small pieces cut from the posterior end. with a rate 

 and vigor at first normal but gradually falling off as the pieces 

 became exhausted. There was, however, a noteable absence of the 

 periods of cessation exhibited in these movements by the intact 

 animal. This points to a possible controlling action of the nervous 

 system, or to the continuous stimulating effect of poor oxidation 

 conditions on the excised pieces. The latter explanation is less 

 probable. Edwards (1909, p. 215) notes that rhythmic movements 

 of the cloaca appear in a very early stage of the free larva of 

 H. floridana, before the respiratory trees are developed. Hence 

 there would seem to be located here an independent mechanism for 

 rhythmic contraction. 



e) Locomotion. With H. surinamensis and rathhuni the force 

 of attachment of the tube feet is never very great, and they may 

 readily be loossened from rocks or the bottom of an aquarium. 

 Indeed, a freeing from attachment to the substratum is one type 

 of reaction to general mechanical stimulation, H. captiva and 

 Stichopus, on the other hand, can rarely be detached without tearing 

 numbers of the pedicel-stalks. This difference in behavior is corre- 

 lated with the nature of the habitats of these species ; H. stirina7nensis 

 generally lives in relatively soft mud, as does rathbuni (though it 

 was found in sand also), while Stichopus occurs freely exposed on 

 harder bottoms and H. captiva was found, even in very young stages 



