176 H. C. STEVENS 



decorating response, recourse was had to the experiment of 

 blinding the crabs. It became evident after the experiments, 

 described in section 4 preceding, had been made that a tactile 

 stimulus may serve as excitant to the response. The relation 

 of the response to the visual and tactile stimuli may be repre- 

 sented by means t)f letters in order to throw more clearly 

 into relief the logical implications of the experiments. Let V 

 stand for the visual stimulus, let T stand for the tactile stimulus, 

 let R stand for the decorating response. In the non-mutilated 

 crab, when R occurs both V and T are present. There are three 

 possibilities as to the relation between R, V and T. V alone 

 may initiate R; T alone may initiate R; or V and T together 

 may initiate R. The experiments with the blinded crabs seemed 

 to show that T alone may initiate R. Whether V alone may 

 initiate R remains to be demonstrated by producing some sort 

 of tactile anesthesia in the legs and chelae without damaging 

 motion. The experiments with blinded crabs seemed to prove 

 beyond doubt that the tactile stimulus alone may initiate the 

 response. Before such a conclusion is warranted, however, the 

 possibility of light receptors other than the eyes must be ex- 

 cluded. It is conceivable that the integument of the crab may 

 respond to light in some such way as does the skin of the frog. 

 To eliminate by experiment this possibility, which indeed seems 

 very remote, blinded crabs were placed in the reaction box and 

 their behavior observed through the hole in the top. Speci- 

 mens 7, 26 and 27 were used. Specimen 26 gave no reaction 

 whatever when placed in the reaction box with red in the left, 

 and yellow in the right, window. Specimens 7 and 27 wan- 

 dered apparently aimlessly about the walls of the box without 

 stopping in front of the windows. It seems certain, therefore, 

 that blinded crabs do not react to light stimuli. 



III. CONCLUSIONS 



1. The color reactions of Oregonia gracilis are determined by 

 the color of the light to which it has been previously exposed. 

 This conclusion is justified by the results of section 2 of our 

 experiments. The result may be explained by supposing that 

 this crab possesses a specific chromo-kinetic resonance, or to 

 state the same fact in other word's, that it acquires a specific 

 chromotropism. This acquired chromotropism may be as- 



