INSECTA 511 



ones, these being reduced in number as compared with the nemato- 

 ceran condition. The maxillary palpi are porrect (not pendulous). 

 Their larvae are hemi-cephalous with vertically biting mandibles and 

 the pupae are free and spiny. From this vast assemblage of flies we 

 may mention the Tabanidae or gad-flies (Fig. 350 B). These flies, to the 

 mouth parts of which reference has already been made, are of stout 

 build and possess large eyes occupying a large part of the head surface. 

 Though a few transmit disease organisms (Chrysops dimidiata, the 

 vector of the worm. Filaria loa is responsible for Calabar swelling in the 

 natives of West Africa), the majority are harmful chiefly through the 

 annoyance which their bites occasion. Tabanid eggs are usually laid 

 on the leaves of plants overhanging water and their carnivorous 

 larvae are either aquatic or ground dwellers. The robber flies (Asilidae) 

 are large bristly flies with a backwardly directed proboscis. They feed 

 on all kinds of insects which they paralyse with their salivary fluid, and 

 their legs, being strong and provided with powerful claws, are well 

 adapted for grasping the prey. 



The Empidae, flies of more slender build, exhibit similar habits. 

 Their larvae are terrestrial as are also those of the preceding family. 



Suborder Cyclorrhapha. These flies emerge from a pupa which is 

 enclosed in the last larval skin or puparium and the commonly trans- 

 verse or circular split in the latter, for release of the adult, gives the 

 name to this suborder. It is therefore really a larval feature which 

 establishes the position of these flies in the classification. 



The antennae are three-jointed, the last of which is greatly en- 

 larged, carrying a dorsal spine or arista. The maxillary palpi are one- 

 jointed and porrect. A crescentic suture on the head lies above and 

 encloses the bases of the antennae. This, known as the frontal suture, 

 is a narrow slit along the margins of which the wall of the head is 

 invaginated to form the ptilinal sac, the eversion of which enables the 

 adult to emerge from the puparium. The extent to which the frontal 

 suture is developed and the ptilinum persists, varies. The Syrphidae, 

 for instance, have usually no persistent ptilinum and the frontal suture 

 is not well-developed. All larvae have a vestigial head, and are either 

 amphi- or metapneustic. 



The Syrphidae (hover-flies) form an important family of brightly 

 coloured flies, whose most obvious mark of distinction is the posses- 

 sion of a false longitudinal vein lying about the middle of the wing. 

 Their larvae are amphipneustic, leathery grubs, some of which 

 devour Aphidae (Syrphus), others hving in decaying material being 

 saprophagous {Eristalis), others again being phytophagous (Merodon, 

 the bulb-fly). 



The remainder may be considered under the heading of muscid 

 flies. The frontal suture is prominent and the ptilinum persists. Many 



