270 



W. J. Crozier, 



and of the amplitude of the reaction as measured by the period of 

 tentacle concealment, show the rhythmic character to which attention 

 has already been called. 



Table A^III. 



"Retraction times" (seconds) to shadow stimuli. 



Exp. 42. July 7. 



Temp. 29,0^. Bright sunlight. Shaded every half minute. Time- 

 given only to the nearest whole second, because of the difficulty of ob- 

 taining accurate points for measurement. 



No. of 

 stimulus 



(1) 



(2) 



(3) 



1 



10 



8 



6 



2 



10 



8 



6 



3 



12 



7 



10 



4 



5 



12 



14 



5 



3 



13 



10 



6 



3 



9 



8 



7 







4 



4 



8 



1 







1 



9 



6 







6 



10 



4 



5 



8 



11 



V 







12 



12 



4 



3 



3 



13 



1 



1 



2 



14 



7 







1 



15 



8 







7 



16 



9 







10 



17 



1 





18 



18 









6 



19 



1 





5 



20 



9 









21 



9 









22 



7 









23 



8 







24 



15 







25 



10 







The shadow reflex was given only within a certain range of 

 temperatures. Holothurians were heated in seawater contained in 

 glass beakers and the temperature at which the shadow reaction 

 ceased was noted. The record of one such experiment is her& 

 given : 



