AND HABITS OF THE YELLOW DUNG -FLY. 



633 



are united posteriorly, forming a U-shaped structure. This space 

 is the oral pit, and the common trunks of the pseudotrachese 

 open into this. 



Up to this point the structure, except for minor details, is 

 identical with that of the Blow-fly or House-fly. In addition, 

 however, the haustellum is strengthened by a pair of long, 

 chitinised rods (text-fig. 2,/), articulating proximally with the 

 fulcrum and distally with the discal sclerites. These occur also 

 in the House-fly and Blow-fly, but are only very slender rods. 



Text-figure 2. 



Mouth-parts of adult : — a, fulcrum ; d, labrum-epipharynx ; e, hypopharynx ; 

 f, rods ; g, furca ; li, discal sclerite ; i, teeth ; j, theca ; k, pseudotrachese. 



They play an important part in the articulation of the oral 

 disc. In this case the oral disc is extremely mobile and used for 

 rasping as well as sucking, therefore the rods are more strongly 

 developed. These rods are called paraphyses by Lowne in his 

 description of the Blow-fly. 



The paraphyses articulate distally with the discal sclerite : thus, 

 there are two articulation points between the haustellum and 

 oral disc — the first between the theca and furca, and the second 

 between the paraphyses and the discal sclerite. 



To each arm of the discal sclerite a set of teeth is attached 

 Pkoc, Zool. Soa— 1920, No. XLII. 42 



