266 



W. J. Ceozieb, 



amputated. The relative "shadow sensitivity" of the various parts 

 studied is roughly shown by the reaction times in Table IV. The 

 relative amplitudes of the reactions are indicated in decreasing order 

 by the numbers (1) . . . (5). The reaction times are the averages 

 of ten sets of observations. The variability of these reactions, as 

 obtained from the numerous animals observed, was very great. 



Table IV. 



Reaction times to sudden shading — in seconds. Temp. 27,5*'. 



Tentacles 



Ant. end^) 



Post, end 



Midbody^) 



Podia^) 



(1) 

 1,2- 



(2) 

 2,0 



(3) 

 1,0- 



(4) 

 2,0+ 



(5) 

 oo? 



1) With the tentacles couipletely retracted. 



2) Only in bright sunlight, and not even then in all animals. 



3) Response toe indefinite to be measured. 



Of all the reactions those of the tentacles were the most clearly 

 defined, and in the experiments made to determine some of the 

 characteristics of this reflex the tentacles were studied exclusively. 



It may first be pointed out that the tentacles on small anterior 

 fragments which had successfully accomplished the closure of the 

 cut end, reacted to shadows in an entirely normal fashion, both as 

 regards the reaction time, and the period during which the brim 

 was closed down, though these isolated pieces were very quickly 

 exhausted (see Tables V and VII). 



Table V. 



Exp. 27.3. 



July 2. Comparison of the shading response of normal tentacles, 

 and of those on isolated anterior pieces. Anterior ends removed 40 hrs. 

 before this experiment. Measurements in seconds. Temp. 25,0*^. 



No. 



Normal 



Reaction time 



1,3 

 2,8 

 2,0 



Period 

 of contraction 



10,0 

 2,0 

 5,0 



Isolated ant. ends 

 Reaction time 



1,9 

 3,0 

 2,4 



Period 

 of contraction 



16,0 



18,0 



2,5 



