ACQUIRED SPECIFIC REACTIONS TO COLOR 161 



In describing the manner in which the crabs behave after 

 being released in the pen with the anterior end facing towards 

 the rear of the box, it was stated that some of the animals 

 moved to the left and some moved to the right corner of the 

 pen. It was shown, furthermore, that the animal sidled along 

 the oblique partition of the pen and finally emerged with 

 the longitudinal axis of its body transverse to the mid-line of 

 the box and with its cephalothorax pointing either to the right 

 or left, so that the right or left half of the body only was exclu- 

 sively stimulated. The question naturally arises whether the 

 side of the body (right or left) which is exposed to the light 

 influence to any extent the window (right or left) to which 

 the animal reacts. An analysis of the reactions with respect 

 to this point shows that out of 198 reactions, the crab emerged 

 from the pen with the head towards the right side of the box, 

 63 times. Of these 63 reactions, 31 reactions were to the light 

 in the right window, and 32 reactions to the light in the left 

 window. The distribution is exactly what one would expect 

 if chance alone were operative. In 135 cases the crab "emerged 

 from the pen with the head directed to the left side of the box. 

 Of the 135 cases, 72 went to the left light and 63 to the right 

 light. Although the figures show an excess of 9 in favor of the 

 left window, the author considers this only such a deviation 

 from the distribution according to chance as is to be expected 

 from a small number of reactions. On the other hand, the head 

 upon emergence from the pen was turned to the right in 63, 

 and to the left in 135, cases. This difference is too great to be 

 attributed to chance. Some influence must have been at work 

 to determine the predominance of the reactions with the head 

 towards the left. This influence might conceivably be resident 

 in the reaction box itself, in the crab or in some circumstance 

 outside of the box. As far as could be seen, the right and left 

 sides of the box were exactly alike. So far as is known the 

 two sides of the body of the crab are identical. Of the circum- 

 stances existing outside of the box, there is the fact that the 

 observer sat upon the right side of the reaction box. It seems 

 likely, therefore, that the observer in some unknown manner, 

 either in placing the crab in the pen or by the mere presence 

 of his body upon the right side of the box, influenced the initial 

 turning of the crab. 



