ORAL APERTURE AND FULCRUM l7 



The Oral Aper'tm-e lies at the base of the small oral pit, 

 which is a space kept open between the oral lobes by means of 

 the discal sclerites. The median pseudo-tracheae do not extend 

 as far as the discal sclerites, but on entering the oral pit th(! 

 chitinous rings cease and are replaced by nairow A-shaped 

 sclerites for a short distance, while the sides of the or;il pit 

 are bordered by a row of teeth, which have been termed the 

 prestomial teeth and which lie at the sides of the openings of 

 the pseudo-tracheal channels. Between the pseudo-tracheae the 

 membranous surface of each oral lobe is thrown, probably in 

 the relaxed state only, into longitudinal sinuous ridges ; there 

 appear to be two such ridges between adjacent pseudo-tracheae. 

 Projecting from the bottom of the furrows are several papillae, 

 generally four or five to each interpseudo-tracheal area, of a 

 gustatory nature, the gustatory papillae (fig. 3, gp.). 



In certain text-books and treatises in which the proboscis of 

 the house-fly is described a misconception of the character and 

 consequent function of the pseudo-tracheae is frequently repeated. 

 The pseudo-tracheae are described as horny " rasp-like " ridges 

 which, by a " rasping " action, remove small particles, of sugar, for 

 example, which the fly can swallow. A careful study of the nature 

 of the pseudo-tracheae and the method of feeding of the house-fly 

 would convince anyone who attempted to verify the above idea 

 of the mistaken interpretation and description. 



The Fulcrum. This chitinous portion of the pharynx (fig. 3, F.) 

 lies on the lower part of the head and in the rostrum. Kraepelin 

 describes it as being shaped like a Spanish stirrup iron. Its struc- 

 ture will be best understood by referring to the figures. It consists 

 of an outer portion, which is U-shaped in section; the basal portion, 

 which is posterior and forms the floor of the pharynx (which 

 Lowne, unfortunately, terms the hypopharynx), is vertical when 

 the proboscis is extended. This basal portion is evenly rounded 

 at both ends, and at the sides of the upper end there is a pair of 

 processes — the posterior cornua (fig. 3, p.c.) which serve for the 

 attachment of muscles. The sides of the fulcrum are somewhat 

 triangular in shape ; their upper anterior portions are produced to 

 form the anterior cornua (a. c.) ; here the sides bend inwards at 

 right angles, and meet below the epistomium, upon which the 



H. n.-F. 2 



