No. 64] DIPTERA OF CONNECTICUT: MORPHOLOGY 37 



(Fig. 4, K and I). The openings between the arms of the forks of the 

 bifid ends of the loops are called the interbitid spaces (/ of Fig. 4, K 

 and I) ; and small grooves on the surface of the labellum open through 

 these interbifid spaces, into the lumen of the pseudotracheae. These 



; interbifid spaces form a filtering apparatus for straining out the larger 

 particles of food when the dissolved food is taken into the pseudo- 

 tracheae (probably through capillarj' attraction), and passes from 

 them into the collecting channels and "oral aperture", to be taken up 

 into the food channel between the labrum and hypopharynx, etc. 



The proboscis is made up of the mouth parts (exclusive of the 

 maxillary palpi), but the labium is by far the most prominent feature 

 in its composition. Tlie proboscis is greatly reduced in Oncodes and 

 Gastrophilus ; and in Oncodes there is no opening of the alimentary 

 tract through it to the exterior, according to Peterson (1916). In 

 most of the higher Diptera the proboscis is readily protruded and re- 

 tracted; and the hinged regions, where the foldings take place, divide 

 the proboscis into characteristic parts, or regions, to wdiich variou.s 

 names have been aj^plied. 



The proximal region of the proboscis, hpr of Fig. 4, B, E and J, 

 is called the oral cone, rostrum, or basiproboscis, and extends from 

 the subcranial or "orar" margin, .07ii of L'ig. 4, B, to the hinge at the 

 proximal end of the prementum, pm of Fig. 4, E. It bears the la- 

 brum, hypopharynx, maxillary palpi and galeae (Fig. 4, A), and con- 

 tains the internal fulcrum and the apodeme-like cryptostipes, or ros- 

 tral apodemes {fu and cr of Fig. 4, E), and is largely made up of the 

 membranous region around the anteclypeus, and that around the men- 

 tum, together with the areas about the maxillae, etc. This portion of 

 the proboscis is hinged above near the dorsal posterior end of the ante- 

 clypeus, ac of Fig. 4. B. and is received into the subcranial cavity of 

 the head (which is usually rather inappropriately called the "oral'" 

 cavity— although the true oral cavity is a wholly different region, for 

 the ingestion of food). The basal region of the proboscis is pro- 

 truded largely by the pressure of the distended air sacs, which col- 

 lapse to make room for the fulcrum, fu, (Fig. 4. B), when this portion 



\ of the proboscis is retracted. The action of the muscles which pro- 

 trude the ''oral cone" is described bv Graham-Smith (1930), Weber 

 (1933) and others. 



The median portion of the proboscis, mpr, extends from the tip of 

 tlie ''oral cone" to the labella, and is called the haustellum, or medi- 

 proboscis. This portion of the proboscis belongs wholly to the labium, 

 and inchides the prementum, pm, posteriorly, while its anterior por- 

 tion contains the labial gutter, or trough, in which the labrum and 

 hypopharynx usually lie. It folds up against the basal portion of the 

 proboscis when the latter is Avithdrawn into the subcranial, or "oral'' 

 cavitv. The muscles operating this portion of the proboscis are like- 

 wise described by Weber (1933^), Graham-Smith (1930), etc. 



The distal portion of the proboscis, called the distiproboseis, is 

 composed of the lal)ella, la, or oral lobes. These are dilated by blood 

 pressure, and are operated by various small muscles attached to the 

 Irtbellar sclerites, etc., which bring about the complicated movements 



