' 



On the structure of the stalked eyes 



in Diopsidae. 



F. 0. EGGERS. 



(From the Zootomical Laboratory of the University of Petrograd). 



Introduction. 



During their journey in Britisli East Africa in tlie summer 

 of 1914 Professor V. Dogiel and I. Sokolov liave collected 

 some material on the anatomy of Diopsidae which they 

 delivered to me for investigation. The mateiial was fixed 

 chiefly with Gilson's mixture, corrosive sublimate and acetic 

 acid and with picric-nitric mixture, and preserved in alcohol. 



Concerning the present work, it contains a description of 

 the peculiar eyes of these flies, the histological investigation 

 of which I undertook by the advice of Professor V. Dogiel. 



Diopsidae, as well as another family, Achiasidae 

 (Cyclorrapha, Acalyptera), are tropical flies distingui- 

 shed by their eyes sitting on long stalks. Amongst insects we 

 find such an arrangement of the eyes only in these forms. 

 In A c h i a s i d a e the stalked eyes are a sexual character, being 

 peculiar to males only. Whereas in Diopsidae both sexes 

 possess stalked eyes (text-fig. A). 



The stalks on which the eyes of the two abovenamed 

 families of Diptera sit present lateral processes of the head, 

 and in many species attain the length of two thirds of the whole 

 body. The eyes are situated at the distal ends of the stalks. 

 In A c h i a s i d a e the eyes alone are removed from the head the 

 antennae remaining on the head. The antennae of Diopsi- 

 dae are displaced together with the eyes to the end of the 

 stalks and are attached somewhat anteriorly to the bases of 

 the eyes (fig. A and figs. 1,2). 



A detailed investigation of the facetted eyes of Diptera 

 was recently undertaken by Dietrich (1909). Although his 



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