EEACTIONS OF LAND ISOPODS TO LIGHT 199 



When the isopod is at rest, the antennae are often spread on the 

 substratum before it. They are frequently moved independently 

 of the rest of the body either just before locomotion begins or, 

 sometimes, at the moment when the animal pauses before chang- 

 ing the direction of its course. When the animal is stimulated 

 by directive light, similar movements of the antennae usually 

 occur before locomotion is started. They are described by 

 Torrey and Hays ('14) as analogous to the so-called 'random 

 movements' of the earthworm or blowfly larva. 



Another common movement of sowbugs, both during ordinary 

 activity and when stimulated, is that of Sviping' or 'cleaning' 

 the antennae. This 'cleaning,' which occurs in other higher 

 Crustacea as well, consists in passing the first walking leg over 

 the antenna as if cleaning it. 



The importance of the antennae is shown further by observa- 

 tion of the locomotion after the antennae are removed. Without 

 antennae, obstructions in the path are not usually avoided until 

 the head or the anterior walking legs come in contact with them. 

 On the other hand, according to Torrey and Hays ('14), "totally 

 blind individuals avoid obstacles with the ease of normal indi- 

 viduals." These results following blinding and removal of 

 antennae indicate that the eyes are not normally used for vision. 



V. EXPERIMENTS WITH DIRECTIVE LIGHT 

 A. APPARATUS 



The experiments were performed in an experimental dark- 

 room in the basement of the Arnold Biological Laboratory, 

 Brown University. A description will be given of the apparatus 

 which was employed after applying the 'trial and error method' 

 to the devising of apparatus. A table, 122 x 75 cm., painted 

 dead black, was placed in the center of the room, under a con- 

 venient overhead light. This table, with space for the ob- 

 server, was surrounded by a black curtain which cut off both the 

 dim light from the ventilator of the room and reflections from all 

 other objects which were not painted black. 



