48 MEDICAL ENTOMOLOGY 



in the higher forms the labella are, therefore, reduced in size, the pseudo- 

 tracheal membrane, no longer required for the absorption of food, disap- 

 pears, and the labium becomes narrowed in its distal part. The muscles, 

 more powerful than those of Musca, are displaced backwards, and are 

 contained in a dilated portion of the labium known as the bulb. To 

 ensure rigidity the labium, which now becomes a piercing stylet, is 

 greatly consolidated, the mentum extends further around the surface, 

 and the labial gutter becomes very much thicker. In the higher forms 

 the posterior joint, by means of which the external labellar wall is drawn 

 backwards and the teeth everted, becomes a very important part of the 

 apparatus. At the same time the joints between the haustellum and 

 the rostrum, and between the latter and the head, remain little altered, 

 and although on account of its increased length the haustellum can no 

 longer be concealed when it is retracted, it is held in the same position 

 as that of Musca, both in use and in repose. In the higher forms the 

 tip of the haustellum projects conspicuously in front of the head when 

 at rest. 



The three species of the genus Philaematomyia at present known show 



separate and early stages of specialization. In all the outward form 



of the proboscis, as well as that of the fly, is identical 



The Genus Philae- ^.^ that Q M usca except in minor points only found 



matomyia . r . . 



by a careful comparison. The proboscis is completely 

 retractile, and possesses a complete and presumably functional pseudo- 

 tracheal membrane. 



In Philaematomyia lineata, Brunetti, the teeth are easily recognized 

 as the homologues of the prestomal teeth of Musca. There are four 

 on each side, each shaped like a rose thorn, attached to the membrane 

 between the terminations of the pseudotracheae by expanded bases, and 

 to the edge of the discal sclerite by their rather elongated distal ends. 

 Like those in Musca, they show evidence of being composed of two 

 lateral portions. The pseudotracheal membrane shows no change except 

 in the smaller number of channels. The discal sclerite is broadened 

 out distally, so that it becomes more V-shaped, and is much stronger. 

 The hypopharynx, which closely resembles that of Musca, is separated 

 completely from the labial gutter, a condition always found in true blood- 

 sucking flies. 



The most important advance in structure in this fly is the separa- 

 tion of the discal sclerite (Plate XII, fig. 2) into two parts, a condition 

 which is found to a much more marked degree in all the other more 

 specialized forms. In lineata all that can be seen is an oblique fissure 



