AND THE SEXUAL DIFFERENCES OF THE EYES IN DIPTERA. 371 



In the Brachycera we again find the chitinous structure more 

 or less developed in the different families. It is very strong in 

 the Asilidae, passes through a complete gradation in the Empidae, 

 being very strong in Clinocera stagncdis, Hal., less in Pachymeria 

 femorata, F., and absent in Hybos. In this latter it is in a 

 similar condition to that found in the specialised Muscidae. In 

 the Dolichopodidae it is never so strong (in the examples in my 

 cabinet drawn from fourteen genera) as in Clinocera, but it is 

 generally easily recognisable. 



In the eyes of a number of species of Phoridae the lenses are 

 bordered by chitinous bands, and a similar condition can be seen 

 in Lonchoptera jlavicauda, Mg. 



In the Leptidae it is markedly chitinous in the genus Leptis, 

 and weaker in Chrysopilus. 



All the preparations of Stratiomyidae I possess have strongly 

 marked chitinous structure. Examples from eight of the 

 principal genera have been examined. 



It is very marked in all the Tabanidae I have examined, with 

 the exception of Chrysopts. But in the male of Haematopota 

 pluvialis, L., I have met with a most striking variation. The 

 lenses differ in size, the lower being much smaller than the upper; 

 and these smaller lenses are strongly defined with chitinous 

 structure. The larger lenses lack this chitin, but between the 

 two sizes we find a small space — a transition area, as it were — 

 which shows the chitin in a degenerating condition (Fig. 8). 



As I have in a former paper in this Journal * suggested (on 

 the evidence of the mouth structure) that this genus is probably 

 close to an ancestral form of the Muscidae ; and as the Muscidae 

 are without these chitinous structures, we can assume that this 

 eye possibly shows the transition stage. The exotic Pangonia 

 longirostris shows a similar structure to Tabanus. 



Bombylius discolor, Mik., <£, shows the chitinous structure well 

 developed, as also does the Cyrtid Oncodes gibbosus, L. 



* "The Proboscis of the Blow-fly," Journ. Qjielctt Microscopical Club, 

 Ser. 2, Vol. 10, No. 63, p. 283. 



