ACQUIRED SPECIFIC REACTIONS TO COLOR 159 



of light and the mid-line of its body coinciding with the middle 

 line of the reaction box. With only one or two exceptions, the 

 first movement of the animal was towards the rear wall of the 

 pen, then to right or left to the corner of the box. On reaching 

 the corner, the animal usually turned to right, if it occupied 

 the right corner, (the observer is supposed to be facing the 

 windows) or to the left, if it occupied the left corner in such a 

 way that long axis of its body was perpendicular to the oblique 

 partitions of the pen and the walking legs on one side of its 

 body in contact with the rear wall of the box. On moving out 

 of the pen, progress was always a sort of side wise sidle along 

 the oblique partition of the pen, with the long axis of the body 

 perpendicular to the wall and the walking legs of the side exposed 

 to the light reaching out along the floor and wall. On emerging 

 from the pen. the long axis of the animal's body was transverse 

 to the long axis of the box, but exactly on the middle line of 

 the box. One side of the crab was, therefore, exposed to the 

 action of the light from the two windows. Since the oblique 

 wall of the pen made an angle of about 45 degrees with the 

 side of the reaction box, it is evident that the long axis of the 

 crab must have rotated through an angle of 45 degrees before 

 it could become transverse to the long axis of the box. Such 

 a rotation did actually take place when the crab arrived at the 

 end of the oblique partition. The posterior walking legs on the 

 side towards the light would reach around the end of the par- 

 tition and swing the body of the crab into a position at right 

 angles to the long dimension of the box. In very rare cases 

 when the crab was very weakly positively phototropic, the 

 movement of rotation w T ould continue until the animal was 

 completely outside the pen but still in contact with the parti- 

 tion, the long axis of its body perpendicular to the partition, 

 as ever. In these rare cases, the animal would sometimes con- 

 tinue its side-wise progress until it occupied the corner at the 

 rear of the box between the oblique partition and the side. In 

 the typical reaction of a majority of positively phototropic 

 crabs, the animal, on emerging from the pen, struck out without 

 hesitation along the middle line of the box until it reached the 

 medial partition between the two windows. Upon contact with 

 the partition, rotation would occur, sometimes with a slight 

 hesitation, usually, however, without, and the animal would 



