76 Studies in Animal Behavior 



the basis of his studies on the light reactions of an- 

 other earthworm, AUolobophora, concludes that "se- 

 lection of random movements, as Holmes, Harper 

 and Jennings pointed out, undoubtedly plays a very 

 large part in the orientation of the earthworm un- 

 der ordinary conditions." The results obtained by 

 Mast in his careful studies of the reactions of fly 

 larvae confirm my own position as to the selection 

 of random movements in these forms and add a 

 number of interesting facts, one of which is that 

 under certain conditions orientation may be to a 

 considerable extent direct. Larvae at first exposed to 

 strong light turn about as often towards as away 

 from it and orientation is effected mainly by the 

 method above described, but after longer exposure 

 the percentage of direct turns from the light in- 

 creases. This is accounted for by Mast, as follows: 

 "If the larvEB are carefully observed when they are 

 suddenly exposed to lateral illumination by diffuse 

 light, it is found that they respond immediately 

 only if the anterior end is turned toward the 

 source of light when the exposure is made. If this 

 end is in any other position, there is no re- 

 action whatever until the organism, in its normal 

 process of locomotion, extends it toward the 

 source of light. Then it is at once turned from 

 the light to such an extent that it frequently 

 makes a right angle with the posterior end. Later 

 it is swung back, but only part way. The tip 

 is, however, exposed and so the animal may be stim- 



