74 Studies in Animal Behavior 



a number of random movements in all directions only 

 those are followed up which bring the animal out 

 of the undesirable situation." 



With the blow fly larvae the method of orienta- 

 tion was much the same. "When a strong light 

 is thrown on a fly larva from in front, the anterior 

 end of the creature is drawn back, turned to one 

 side and extended again. Often the head is moved 

 back and forth several times before it is set down. 

 Then it may set the head down when it is turned 

 away from the light and pull the body around. If 

 the head in moving to and fro comes into strong 

 light it is often retracted and then extended again 

 in some other direction, or it may be swung back 

 without being withdrawn. If a strong light is thrown 

 on a larva from one side it may swing the head 

 either towards or away from the light. If the 

 head is swung towards the light, it may be with- 

 drawn or flexed in the opposite direction, or, more 

 rarely, moved towards the light still more. If it is 

 turned away from the light the larva usually follows 

 up the movement by locomotion. Frequently the 

 larva deviates considerably from a straight path, 

 but as it continually throws the anterior end of the 

 body about and most frequently follows up the move- 

 ment which brings it away from the stimulus, its 

 general direction of locomotion is away from the 

 light. In very strong illumination the extension of 

 the anterior part of the body away from the light 

 is followed by a retraction, since in whatever direc- 



