404 Transactions of the Society. 



general appearance and detail of some of their limbs, as well as 

 the armature of the mouth, might be thought to be raptorial, were 

 it not that the convincing evidence afforded by the contents of 

 their stomachs exonerates them — (Ascia, Erystalis, Heliophilus, 

 Mallota, Xylota, and Syritta). In some of the genera of the 

 Ephydridae, there is a serrated fore femur, the chitin itself being 

 drawn out into a number of sharp teeth, exactly like those of a 

 saw ; this is unusual, most of these contrivances consisting of 

 strong hairs in sockets. 



d. Secondary sexual. — These structures are more strikingly 

 developed, and more commonly found in the male sex ; they 

 mostly consist of an extraordinary variety of modification of the 

 legs, usually of one particular pair, and often of the abdomen. 



Setse are altered in shape and grouped in rows ; they are, as a 

 rule, blunter than those found on the raptorial limb, and occa- 

 sionally take the form of bunches or pads of quite soft hair. 

 Sometimes a seta is provided with a round head, not unlike that 

 of the ordinary pin. In many cases the shapes of the tibiae are 

 modified, and more often the tarsi are greatly enlarged, spatulated 



EXPLANATION OF PLATE VI. 



Fig. 7. — Hind leg of Leptogaster cylindrica Deg. ? . Raptorial type. Belongs 

 to the Asilidae, the most predaceous family in Diptera. 



Fig. 8. — Fore leg of Hilara clypcata Mg. <$ . To illustrate the secondary 

 sexual type. The extraordinarily enlarged metatarsus is used in holding the 

 female, whose fore leg is quite simple. The Hilaridcc mate while flying, belong 

 to the predaceous Empidae, and are found over streams or brooks. 



Fig. 9. — Fore leg of Hydrotea parva Mde. 6 ■ Secondary sexual type. The 

 males of this genus of the Anthomyidse, are easily recognised by the remarkable 

 modifications of the fore femora and tibia. In the Hydrellinse the fore femora of 

 both sexes is elaborated for predatory purposes. In Hydrotea only that of the 

 male, and for sexual advantage. These insects are found in gardens and on 

 hedges, and appear to be general feeders like the Blow-fly. 



Fig. 10. — Middle leg of Dolichopus plumipes Scop. 6 . Secondary sexual type. 

 Belongs to the family of the same name, and is predaceous. The fine tomentum 

 on the tarsi of many genera enables the insect to glide on the surface film of 

 shallow undisturbed water. This particular species is however met with on 

 damp herbage. 



Fig. 11. — Hind leg of Ophyra leucostoma W. <$ . Secondary sexual type. 

 Belongs to the Anthomyidse, and from the venation of wing, the shortness of the 

 labium, and the marked remains of the maxillary palpi, may be thought to be of 

 a far more primitive form than any of the Muscidae proper, except the Cyrtoneura 

 group. Every joint of this leg is modified for sexual purposes. The femur has 

 numerous hairs and stiff bristles ; the tibia is curved and ciliated with a soft 

 pad or brush of hair, and the inner sides of the tarsi are clothed with delicate 

 pubescence. The food consists of pollen and minute vegetable organisms. 



Fig. 12. — Fore leg of Melophagus ovinus L. 9 . Parasitic type. This insect is 

 found on sheep, and is sometimes wrongly called the " sheep tick." The claw is 

 characteristic of the family, the Hippoboscidae, and is well adapted for fastening 

 on to the fleece of the host ; so much so that I have had, on occasion, some 

 trouble in detaching hair from it. 



Fig. 13. — Fore claw of Culcx pipiens L. 6 ■ This is a secondary sexual charac- 

 ter. A comparison of the claws figured will give an idea of the habits of the 

 insects. 



