REACTIONS TO LIGHT IN VANESSA ANTIOPA 363 



reactions under the former conditions seem to indicate that 

 both eyes are necessary for orientation; those under the latter, 

 that only one eye is necessary. Consequently, if the butterflies 

 had been studied only in front of a window, the conclusions 

 would necessarily have been erroneous. 



Circus movements have been held by many to have a very 

 important bearing on the question as to the nature of the process 

 of orientation. 



Holmes discusses this question rather fully. He takes the 

 position that the performance of circus movements indicates a 

 direct or indirect connection between the impulses set up by 

 light in the two retinas and the tension of the muscles of the 

 legs or appendages on the two sides of the body, and that this 

 is a "sort of mechanical reflex process." To him the pleasure- 

 pain theory explains those cases in which orientation occurs 

 in these asymmetrical animals. He says ('11, p. 54): "In most 

 Crustacea, as in most insects, orientation is effected through the 

 unequal action of the appendages on the two sides of the body. 

 In a form which is positively phototactic, light entering one eye 

 sets up impulses, which, passing through the brain and nerve 

 cord, cause, directly or indirectly, movements predominantly of 

 flexion of the legs of the same side and of extension of the append- 

 ages of the opposite side of the body. If this is a sort of mechani- 

 cal process, we should expect that, in a positively phototactic 

 form, if one eye were destroyed or blackened over, the animal 

 would move continuously toward the normal side." Mindful 

 of the fact that the Ranatras and Notonectas in time straightened 

 their courses, and followed the light nearly as precisely as if they 

 had the use of both eyes, he also concludes that "Phototaxis 

 may fall, to a certain extent, under the pleasure-pain type of 



behavior Light, in some animals, is followed much 



as an object of interest is pursued by a higher animal" ('11, 

 p. 55). To these conclusions Brundin ('13) assents. 



According to Carpenter, the local action theory of tropisms 

 would explain circus movements, were it not that some animals 

 with one eye blackened can orient as accurately as if both eyes 

 were functional. The pleasure-pain theory, he holds, explains 



