MOUTH PARTS 19 



certain muscles attached at its base. There is no arista like that of the 

 Muscid flies, but at the tip of the scape there are several stout forwardly 

 directed bristles which probably represent it. The antennae and the pit 

 in which they lie are of the same leathery consistence as the rest of 

 the integument. 



THE MOUTH PARTS AND SUCKING APPARATUS 



It is characteristic of the Diptera that the mouth parts are adapted for 

 sucking, and in the blood-sucking forms they are also modified to form a 

 piercing organ. As it is through the mouth that all blood parasites must 

 pass, either to or from the host, a detailed consideration of the region, 

 and of the mechanism by which the parts act, is necessary. As a 

 matter of convenience the first part of the alimentary canal, which is 

 modified to form the sucking apparatus, will also be described here, for 

 it is so intimately connected with the mouth parts both in function and 

 in structure that the two cannot be satisfactorily considered separately. 



The mouth parts project beyond the head, and form a more or less 

 cylindrical bundle, termed the proboscis. Its shape, relative length, and 

 the position in which it is held, are of importance in systematic work. 

 It may be cylindrical and of approximately the same diameter throughout, 

 as in the mosquitoes, or swollen at the base and pointed distally, as in 

 Stomoxys ; or cylindrical and thick with a joint in the middle, as 

 in the house fly and its near allies. It may be short and inconspicuous, 

 as in Simuliiim and Ceratopogon, or very long, as in many mosquitoes. 

 The position in which it is held varies from the horizontal to the vertical, 

 as, for instance, in the Anopheline mosquitos and the Tabanidae. It may 

 be straight or curved. In the non-biting Muscid flies, and in the genus 

 Philaematomyia, it is completely retractile ; in Stomoxys and in Glossina 

 only partially so. In Hippobosca almost the whole of the proboscis 

 can be withdrawn within the head. 



The constituent parts of the proboscis, excluding the wall of the head 

 capsule when it takes part, are enumerated as follows : 



The Labrum, or upper lip. 



The Epipharynx, usually combined with the labrum. 



The Hypopharynx. 



The Mandibles, appendages of the fourth segment of the head. 



The First Maxillae, appendages of the fifth segment. 



The Labium, or lower lip, composed of the appendages of the sixth 

 segment, fused together except at their distal ends. 



