308 



W. J. CROZIER 



The rate of rhythmic pulsation of the anal sphincter for ani- 

 mals of different sizes was observed in Stichopus, Holothuria 

 surinamensis, H. captiva, and Cucumaria punctata. The results 

 are given in figures 6 to 9. The data in the case of Stichopus 

 (fig. 9) are more irregularly distributed than with the other 



Relation between size and pulsation-rate 



6 cm. 



Fig. 6 Cucumaria punctata. Temp. = 24. .5* 



5 6 7 8 9 10 II 12 13 Cm. 

 Fig. 7 Holothuria surinamensis. Temp. 25.0° 



forms. This is due to the fact that in the instances measured 

 the individuals of the other species were of more homogeneous 

 history, in that their small size made it possible to keep numbers 

 of them in a single aquarium, so that their pulsation rates were 



