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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 52 



later ascertained that most of the larvae, when about ready to pupate, 

 became photonegative. These were sluggish in action, were deeper 

 yellow in color, and their intestines usually were not visible through 

 the integument as they are in the more active larvae. 



Hundreds of adult bean beetles, including the overwintering ones, 

 those of the second and third broods, and many ready to hibernate, 

 were tested in one way or another. Practically all were found to be 

 photopositive, most of them being strongly so (fig. i, e). At no time 

 were photonegative beetles observed. The nearest approach to this 



Fig. I. — Diagram of phototactic box and tracings of tracks of Mexican bean 

 beetle, illustrating responses to light of this insect. The tracings are as follows: 

 a, larva just hatched; b, larva of second instar ; c-, larva of third instar; d, larva 

 of fourtli instar ; and c, adult ready to hibernate. 



condition was found among old ones of the second brood, but when 

 repeatedly tested it was decided that they too were still photopositive. 



(b) description of dark-room and apparatus 



Since it is often difficult to separate phototactic res^xjnses from 

 geotactic ones, special apparatus is then necessary. Not having a 

 dark-room whose temperature and relative humidity could be con- 

 trolled, an attempt was made to construct one by using a room, lo 

 feet long, 9 feet wide, and 9 feet high. It was made totally dark as 

 follows : Boards were nailed to the wooden shutters which closed 



