246 W. WESCHE ON MODIFICATIONS OF LEGS IN DIPTEROUS FLIES. 



spurs, and strong spines, for the better holding of prey or 

 mate. I will give first a few examples of legs modified to 

 hold prey. 



Passing over the forelegs of Bihio and DilopTius^ which may 

 be seen figured in many books, I may remark that, as they are 

 to be found in both sexes, they are probably used as offensive 

 weapons. I have figured the middle leg of Tachydromia arrogans 

 (Curtis), of the family Empidae (Fig. 1). Not only are the hairs 

 in this species modified into sharp spines, but the femur is 

 thickened, probably to contain a strong muscle, and the tibia has 

 its end hardened and pointed, and is used to pierce the body of 

 the victim, while the toothed femur and tibia grasp the wings 

 and thorax. 



Belonging to the same family is Hyhos femoratus. In this 

 species it is the hind leg which has been modified (Fig. 2) ; 

 the tibia is not toothed or sharpened, but the first tarsus and 

 femur are strongly armed. 



There is doubt as to the use of the adaptations in the two 

 following examples. The hind legs of Ascia j^odagrica (Fig. 3) are 

 of the same type as the two preceding species, but the habits 

 of the flies are totally dissimilar. Ascia is a genus of the 

 Syrphus flies, better known as Hawk or Hover flies : they are 

 pollen feeders. Many genera have in both sexes the hind femur 

 enlarged and studded with strong teeth or spines. I have seen 

 the contents of the stomachs of a number of species, and have 

 always found pollen only. 



The strong hooks on the end of the tibiae of the hind legs of 

 Sphaerocera suhsaltans are also difficult to explain, but they are 

 probably offensive weapons. The tarsi are also much modified, 

 and the two upper are furnished with pads of soft hair 

 (Fig. 9). 



We now come to those adaptations which are to be found 

 only in the male, and are known as '' secondary sexual 

 characters." 



The middle legs of Cainpsicneiinus curvipes are most elaborate 

 in detail (Fig. 4). The shapes of the femora, tibiae, and first tarsi 

 have all been altered to enable the limbs to obtain a firmer hold 

 of the abdomen of the female. Many strong hairs and spines 

 have been arranged on the depressions and grouped for the same 

 purpose. Ca/nipsicnemus is a genus of the family Dolichopidae, 



