EHYTHMIC PULSATION 325 



derived from their contraction is transmitted posteriorly ^^ by 

 the integumentary nerve-net, while the wave of opening travels 

 posteriorly along the cloaca, until finally the anal sphincter opens. 

 Upon the contraction of the sphincter a wave of constriction 

 travels anteriorly on the cloaca, forcing out the contained water. 



IV. RELATION OF PULSATION TO TEMPERATURE 



The large size of Stichopus precluded any attempt to employ 

 the entire animal in a series of temperature experiments, both 

 because there were no large thermostats available and because 

 the thickness of its integument is prejudicial to the rapid estab- 

 lishment of uniform temperature conditions throughout the ani- 

 mal. For these tests therefore I employed Holothuria suri- 

 namensis and H. captiva; they were subjected to temperature 

 changes in beakers of thin glass contained in a heating or cooling 

 bath. Temperatures were measured by an enclosed-scale ther- 

 mometer reading to 0.01°, placed close to the cloacal end of the 

 animal. The instrument was calibrated. The results of one 

 experiment, typical of all others, are given in figure 22. 



This curve is entirely characteristic of the temperature curves 

 found in connection with many other biological phenomena, in 

 that it is of an exponential character, with a temperature coeffi- 

 cient (12.5°-22.5°) of about 2.4 ±. 



In attempting to obtain temperature coefficients of pulsation 

 rate in the case of the amputated cloacal ends of Stichopus, 

 there entered a very considerable time factor. The method of 

 procedure consisted in (1) obtaining records of rhythm in pieces 

 which had recovered from operative shock and were subjected to 

 fairly slow temperature changes (table 6), and (2) in subjecting 

 similar pieces to sudden changes of temperature and estimating 

 rhythm-rate after 5 to 10 minutes had passed and thermal 

 equilibrium had presumably been established (table 7). The 



1^ Experiments on Stichopus confirm the results obtained with H. surinamensis 

 (Crozier, '15 [?]), to the effect that the responses to sensory stimuli in the pos- 

 terior region of the animal tend to be conducted posteriorly toward the anus, 

 which often reacts before there is visible any local response to the stimulating 

 agent. 



