132 W-. J. CROZIER. 



The respiratory value of the water moved by the cloacal pump 

 is clearly evidenced by this fact : seawater in which a Stichopus 

 was living had a reaction of pn 8.2 ; the pn of the water expelled 

 during spouting was 7.8 ; that of the fluid within the body-cavity, 

 7.6. It is obvious that even within a minute's time relatively con- 

 siderable quantities of CO 2 are able to diffuse across the thin 

 membraneous wall of the distended respiratory trees. According 

 to Winterstein ('09) about 50 per cent, of the respiratory loss of 

 CO 2 is accomplished through the " trees." 



CITATIONS. 

 Arey, L. B., and Crozier, W. J. 



'19 The Sensory Responses of Chiton. Jour. Exp. Zool., Vol. 29, pp. 157-260. 

 Crozier, W. J. 



'16 The Rhythmic Pulsation of the Cloaca of Holothurians. Ibid., Vol. 20, 



PP. 297-356. 

 Hecht, S. 



'16 The Water Current Produced by Ascidia atra Lesueur. Ibid., pp. 429-434. 

 Henri, V. 



'03 fitude des contractions rythmiques des vaisseux et du poumon aqueux 



chez les Holothuries. C. R. Soc. Biol. Paris, torn. 55, pp. 1314-1316. 

 Iwanzoff, N. 



'97 Muskelelemente der Holothurien und ihr Verhalten zum Methylenblau. 



Arch. mikr. Anat., Bd. 49, pp. 103-113. 

 Parker, G. H. 



'14 On the Strength and the Volume of the Water Current Produced by 



Sponges. Jour. Exp. Zool., Vol. 16, pp. 443-446. 

 Putter, A. 



'07 Die Ernahrung der Wassertiere. Zeits. allg. Physiol., Bd. 16, pp. 65-114. 

 Winterstein, H. 



'09 Uber die Atmung der Holothurien. Arch. Fisiol., Vol. 7, pp. 33-4- 



