344 THORBORG MARIE BRUNDIN 



environment is determined by the thigmo tactic sense. In the 

 case of the two Orchestias upon which I experimented, the 

 contact stimulus must be enhanced by moisture, or it will call 

 forth no response. When I place moist filter paper in a dish, 

 the most positive specimens will eventually come to it, and 

 become immediately indifferent or negative to the light. It is 

 for this reason that they will still react positively to the light 

 even when placed in a condition of absolute contact. If I moisten 

 the surface of the glass plate, the creature will stop immediately, 

 curl up and pay no attention to the light for as long as five 

 minutes at a time, the length of the period of rest depending 

 upon the amount of moisture and the position of the specimen 

 with reference to the light. A specimen facing the light may 

 become restless and leave the moisture. 



When one considers the habitat of 0. traskiana, it does not 

 seem inexplicable that it should be able to travel on its side. 

 It usually lies curled up on its side, holding on to the seaweed 

 with its feet. When disturbed, it glides away on its side. 0. 

 pugettensis cannot move between glass plates. The form of 

 its body does not allow movement in such a position. 0. tras- 

 kiana has a compressed body, very fitting for its hiding places, 

 while 0. pugettensis has a round body, suitable for getting into 

 burrows. 



In performing experiments upon the behavior of O. traskiana 

 between plane surfaces, I took a plain glass plate about six 

 by ten inches, and pasted strips of cardboard on the sides in 

 order to raise it sufficiently from the table or lower surface to 

 allow movement of a medium sized O. traskiana. The lower 

 surface consisted of a plate of ground glass, or any hard, slightly 

 rough material. I left a small space of about three-fourths of 

 an inch in the middle of the lower six-inch side of the plate, 

 to be used as the point of entrance. This was made wide enough 

 to allow the creature free movement in pushing itself in. After 

 a specimen had been placed in the entrance, I sometimes blocked 

 it with a piece of paper so that it would be forced to go under 

 the plate. This was not necessary in most cases, as the creature 

 slipped under the plate very readily. In doing so, it went over 

 on its side and traveled by pushing itself by the legs against 

 the glass plates. Specimens set out in the direction of the 

 light in almost every case, but they could not always keep 



