WALTER E. GARREY 109 



Most of the commoner flies {Musca, Dexia) show reactions, when 

 one eye is blackened, which are completely in accord with those shown 

 by Proctacanthus and butterflies, and the general description already 

 given will sufiice, but the banded-eyed fly or "green-eye," Tahanus, 

 is the most typical and sensitive in its responses. All the postural 

 changes already described are well exhibited by this fly, especially 

 the lateral flexion of the broad thin head. After blackening one of 

 its eyes the circus motions toward the unblackened eye are made in 

 circles of very narrow diameter, so that this fly is well adapted to the 

 study of effects of the intensity of hght, to turntable experiments, 

 and incidentally to the study of nystactic movements of the head, 



Fig. 4. Butterfly seen from the front. Shows the tilting of the body and rota- 

 tion of the head toward its left after blackening the right eye. 



which occur in this insect when it is rotated in both directions, even 

 after the eye has been blackened. The nystactic movements are so 

 easily elicited in this fly, and some others observed by the writer, 

 that they are produced by its own spontaneous movements to either 

 side. The drone fly, Eristalis, also shows marked changes of muscle 

 tonus and forced movements due to differences in the illumination 

 of the eyes. To produce the typical results of blackening one eye as 

 seen in other forms, it is necessary, in this insect, also to blacken the 

 inner half of the other eye.'^ When this is done Eristalis shows 



^- Several forms did not exhibit typical results after blackening one eye; for 

 example, the vespidae and dragon flies. Calliphora also is atypical in its reactions, 

 and Eristalis seemed to fall into the same group. It was found on Eristalis that 



