THE PHOTIC REACTIONS OF SARCOPHAGID FLIES 185 



not distributed equally over the entire body of the fly larva, 

 indeed Loeb ('90) has demonstrated that the anterior portion 

 of the larva is most sensitive. Consequently it is highly important 

 to locate definitely if possible the seat of the receptive organs in 

 the sarcophagids. 



When the imago emerges from the pupa case it has well devel- 

 oped organs of sight ; viz. a pair of prominent compound eyes and 

 three ocelli situated dorsally between them. The compound eyes 

 of insects are regarded as image-forming organs, while the ocelli 

 are often only direction eyes, analogous to the eyes of planarians, 

 for example. Further experimental evidence with regard to these 

 matters might well be secured from the flies in question. 



Finally, it will be recalled that Luciha caesar is essentially a 

 fly of the out-of-doors, while Calliphora vomitoria frequents 

 houses as well. Is there any relation between this difference in 

 habit and the intensity of light to which the adults react? 



These questions will be dealt with in the following pages. 



2. Methods 



Eighteen adults of Lucilia caesar collected October 1, 1907 

 formed the nucleus for the winter's supply of this species. From 

 these adults (Lot no. la) five sets of larvae were obtained, viz. 

 Lots nos. 2a, 3, 4, 5, and 6, the eggs having been deposited 

 October 9, October 12, October 20, October 29, and November 1 

 respectively. Lot no. 5 proved to be the only successful one 

 and from this a continuous colony was established for winter 

 use. A continuous colony of Calliphora vomitoria was easily 

 estabhshed from eggs deposited indoors by one adult female. 

 Usually from two to six lots of adults of the two species were kept 

 on hand, so that eggs and larvae were obtainable throughout the 

 winter. The room in which the colonies were housed was con- 

 stantly heated. The flies were exposed to the sunshine whenever 

 available, which was an important factor in securing eggs. 



The experimental work was carried on in a large basement 

 dark room of the Museum of Comparative Zoology. Light inten- 

 sities were measured and calculated in the usual manner with the 

 aid of a Lummer-Brodhun photometer. * 



