490 ^Journal of Comparative Neurology and Psychology. 



Mainly through the recent writings of Jennings attention has 

 been directed to the relative importance and widespread occur- 

 rence of "trial and error" behavior among the lower animals. 

 This kind of behavior is characterized by a repetition of "random 

 movements," certain of which, under ordinary circumstances, 

 are selected and followed up to the advantage of the organism. 

 The convulsive reflex of Drosophila appears to be an instance of 

 behavior of this character, in which, under excessive stimulation, 

 random movements are made with extraordinary vigor and 

 rapidity. There is, however, little evidence of the selection and 

 repetition of those movements which carry the insect in favorable 

 directions. Escape from the stimulating region seems to depend 

 on chance alone. 



The haphazard "trials" that are made during the convulsive 

 reflex are the result of a complex reaction which seemingly involves 

 all the movements of which the animal is capable. Mast ('03) 

 saw in planarians subjected to a high temperature nearly all the 

 reactions the worms have at their command appearing one after 

 another. In Drosophila, with its more highly organized and 

 specialized nervous and muscular organs, the reactions are simul- 

 taneous, each movable part performing its special function to the 

 limit of its capacity. 



Summary, i. Drosophila is negatively thermotropic to high 

 and low temperatures. 



2. When one eye is covered so that the light stimulus is uni- 

 lateral, Drosophila moves toward the source of light in a fairly 

 direct path, but tends to deviate toward the side of the functional 

 eye. A "pleasure-pain" reaction appears to inhibit and dominate 

 a "tropic" reaction. 



3. A violent, uncoordinated motor reaction or convulsive 

 reflex may be induced in Drosophila by stimulating the insect 

 either by a high temperature, or by a low temperature, or by 

 intense light, or by the vapors of such irritating chemical substances 

 as ammonia and acetic acid. 



4. The convulsive reflex thus obtained in Drosophila may be 

 regarded as an instance of trial and error behavior, characterized 

 by a complex of vigorous random movements, involving, apparently, 

 all the movable parts of the insect's body. The escape of the 

 insect from the region of stimulation appears to depend on chance. 



