272 



W. J. Ceozier, 



in the retraction of the appendages and the closure of tlie 

 valves; these become less complete as the stimuli succeed one 

 another. The time taken to reopen the valves, after they had 

 hegun to close as the result of the shadow, is given to the 

 nearest whole second. Exhaustion was more rapid at higher 

 temperature and in brighter light. 



June 21, 



Table IX. 

 The shading reflex in Balanus. 



Exp. 4.15.2. 

 Retraction time, sees. Shaded at one-lialf minute intervals. 







Diffuse light. 







Bright sunlight. 





No. of 

 stimulus 





Temp. 25,10 







Temp. 30° 







(a) 



(b) 



(c) (d) 



(e) 



(f) 



(g) 



(h) 



(i) 



(j) 



1 



15 



20 



26 



25 



19 



7 



27 



12 



5 



9 



2 



9 



10 



12 



23 



4 



7 



11 







1 



10 



3 



45 



34 



7 



24 



9 



11 



60+ 







1 



14 



4 



2 



60+ 



5 



21 



8 



8 















6 



5 



7 



27 



10 



22 



7 



6 















3 



6 



45 



60+ 







38 



3 



7 















1 



7 







5 







27 



26 



3 

















8 















28 



60+ 



5 













9 



40 



17 



5 



20 



3 



4 









5 



10 







5 







45 



44 



1 













11 







12 







22 

















60+ 



12 







40 







23 





















13 



5 



45 







12 







4 













14 















52 





















15 





















2 













16 





























Note. When the reaction occupied more than 0,5 min., one stimulus was 

 omitted. 



In each of the above instances there is a noticeable rise in 

 responsiveness during the first few stimulations. It is possible that 

 this is to be accounted for (as Loeb [1912, p. 46J has explained the 

 more rapid heliotropic movement of aphids after several trials) by 

 the action of the products of muscular fatigue — in other words, as a 

 treppe phenomenon. But a different partial interpretation is possible 

 from the standpoint of a photochemical conception of light stimulation. 



It is sufficiently obvious that it is not the "shadow" which 

 stimulates, but a reduction of the intensity of the incident light. 



