224 BRADLEY M. PATTEN 



the species, a detail which has been too often neglected in work on 

 behavior. Though the species he worked on especially, Lucilia 

 caesar, and Calliphora vomitoria, reacted essentially in the same 

 manner, the former was noticeably more sensitive to light than 

 the latter. Similarly with various Planaria, Walter ('07) has 

 shown well defined species differences in the light response. To 

 avoid inconsistencies which might arise by the neglect of species 

 differences, except for some preliminary experiments, the work 

 was done with the larvae of a single species, Calliphora erythro- 

 cephala Meigen. 



The larvae do not acquire their maximum sensitiveness until 

 the end of the feeding period (Pouchet '72; Herms '11) ; as they ap- 

 proach the pupal stage they became sluggish, and if not actually 

 less sensitive, are certainly very tedious to record. The most fa- 

 vorable age to make the light tests appeared to be at about the 

 time of transition from the feeding to the migratory stage. 



Like many other forms, the larvae soon become acclimated to 

 light, and are much more sensitive if kept from one to three hours 

 in the dark. But a long isolation from food and moisture tends 

 to make them sluggish and to hasten the pupal stage. The best 

 procedure is to keep the whole culture in the dark and not remove 

 the larvae until immediately before they are to be used. 



2. Variability of response 



There proved to be a wide range of individual variability in the 

 response to light, the behavior of a few of the larvae being so 

 characteristic that they could be easily recognized by their re- 

 actions. For example, one larva had a preliminary exercise 

 that it performed with great precision in each one of the experi- 

 ments in which it was used. When placed with its anterior end 

 away from the light, in the small wooden groove in which the 

 larvae were started, this larva looped its anterior end directly 

 back toward the light underneath its own body, until the 'head' 

 emerged from under the posterior end and was struck by the full 

 intensity of the orienting light ; whereupon it promptly uncurled 

 and crawled away from the light, responding otherwise like 

 ordinary larvae. Out of several hundred larvae observed, I 



