RHYTHMIC PULSATION 



329 



factor which renders valueless for exact purposes much of the 

 experimental evidence concerning the influence of temperature 

 upon marine animals (e.g., as in the paper of Mayer, '14 ''); it 

 is simply incorrect to say that an animal dies at such and siich 

 a temperature, for it dies at T° after being heated thereto at a 

 certain rate and kept at T° for a certain length of time. 



S.^0- 



Temperature. 



The curves (figs. 23 and 24) show that there is a rather sharp 

 maximum of pulsation rate in the neighborhood of 26°. No 

 pulsation was apparent below 12.5°, nor above 32.0°. These 

 hmiting temperatures hold for the rates of heat change, etc., 

 used in these experiments; there is no more a definite upper 



THE JOURNAL OP EXPERIMENTAL ZOOLOGY, VOL. 20, NO. 3 



