PROBOSCIS OF PHILAEMATOMYIA 49 



running from the internal border of the looped portion of the sclerite, 

 at the junction of the distal and middle thirds, to the posterior end. 

 The sclerite is thus separated into a distal part, which may at once 

 be termed the axial apophysis, including the apex of the sclerite and 

 a small portion of each lateral side ; and a proximal portion, including 

 that part which bears the teeth and the rods to which the muscles are 

 attached. The posterior elongated portions may be termed the labellar 

 rods, and the raised flange which bears the teeth the tooth plate. The 

 importance of these distinctions will be seen presently. 



The next species, Philaematomyia gurnei, Patton and Cragg, 

 (Plate IX, fig. 7) has six well developed teeth and two smaller ones on each 

 side. Each tooth (Plate VIII, fig. 5) has the same general shape as those 

 of the last species, but is thicker, more deeply pigmented, shorter, and has 

 a more expanded base. The bases of the teeth are not united directly 

 to the discal sclerite, but are attached to the membrane by their bases. 

 They are pressed more closely together, their proximal limits forming a 

 curved line which corresponds to that of the tooth plate ; the teeth on each 

 side, in fact, fit into the cup-shaped depression in the side of the sclerite. 



The discal sclerite is a thick and heavily pigmented structure, in which 

 two parts are clearly differentiated ; the axial apophysis is a stout conical 

 piece, the distal end of which is free ; the labellar rods are very strong, 

 and are wedge-shaped, the broad ends of the wedges being directed dis- 

 tally, and attached by their internal borders to the axial apophysis. The 

 apophysis thus comes to lie between the two labellar rods, its distal point 

 being on about the same level as the termination of the tooth plate. 



The labial gutter in this fly is a thick and densely pigmented structure, 

 which must materially assist in keeping the proboscis rigid under strain. 

 Its articulation with the sclerite, which is placed in a position exactly 

 corresponding with that of Musca, is much more defined. On the 

 upper two-thirds of the posterior surface of the gutter there is a median 

 backward projection, extending into the cavity of the labium and divid- 

 ing the latter into two halves. This is the 'keel' of the labial gutter, 

 and is developed mainly to provide attachment for the muscles which act 

 upon the anterior joint. 



The method of termination of the pseudotracheal channels in this 

 species should be particularly noted, for it furnishes the explanation of 

 much more complex structures in the higher forms. The rings become 

 elongated near the border of the sclerite, and divide in the middle line, 

 the parts being of unequal length and placed one in advance of the other. 

 As the sclerite is approached, the segments become longer and more 

 7 



