306 W. J. CROZIER 



anal sphincter.^ Closure of the anus was also a preliminary 

 operation when Stichopus was beginning to engage in locomotion. 



The control of anal rhythm by the animal as a whole includes, 

 then, (1) the cessation of pulsation by causing the anus to 

 constrict (either in response to stimuli, or in locomotion), and 

 (2) the great restriction of the amplitude of pulsation (in 'spout- 

 ing') due to the contraction of the radiating muscles and the 

 muscles of the body. Of these modes of control only one, con- 

 traction in response to stimulation from the outside, persists in 

 the isolated cloaca. 



As regards the function of cloacal pumping in holothurians, it 

 is clear from the work of Bordas ('99) and Winterstein ('09) 

 that the water drawn in and out of the respiratory trees serves 

 to supply the coelomic fluid with oxygen, to remove excretory 

 products, and at the same time to control the amount of fluid 

 contained within the animal, upon which its locomotor move- 

 ments depend.^ In connection with the respiratory function of 

 pulsation it is of interest to note that if by repeated mechanical 

 stimulation, pulsation is prevented from occurring for some min- 

 utes, the movements which occur when pulsation is resumed 

 are not increased in rapidity, but are of greater amplitude than 

 those normally seen in undisturbed specimens. This was also 

 noted by Pearse ('08, p. 272) in the case of Thyone, and he drew 

 the conclusion that the animal was in this way making up for 

 its preceding oxygen deficiency. This deduction by no means 

 follows, however, because when repeatedly stimulated holothu- 

 rians decrease greatly in volume (cf. Crozier, '15) by expelling 

 water from the anus, and when left undisturbed after such 

 stimulation they tend to return to their original size. In doing 

 this the first pulsations of the new series are more vigorous than 

 usual, as is also found after each normal water expiration. The 

 increase in amplitude observed after forced cessation of pulsa- 

 tion is therefore only remotely connected with respiration; this 



8 These reactions were similar in every respect to those of the previously 

 described H. surinamensis (Crozier, '15 [?]). 



' The movements of holothurians have recently been analyzed by Jordan ('14) 

 from the standpoint of his conception of a 'Hohlorganartig' animal. 



