THE 



Section II. The Proboscis. 

 PLATE II. Figs. 315. PLATE III. 



The proboscis is one of the most remarkable and complex 

 structures found in the insect world ; it consists of three joints, 

 each of which represents a distinct segment. Its hard parts are 

 the homologues of those usually found in the mouths of insects, 

 and although they are greatly modified to serve special purposes ? 

 yet, owing to the elongated nature of the organ, the several 

 segments are perhaps more decidedly distinct in the fly than in 

 any other insect. 



The integument of the basal joint consists chiefly of a funnel- 

 shaped membrane continuous with the antennal segment around 

 the oral cleft ; a semi-transparent trapezoidal plate of chitiue, 

 the epistoma, which forms a hinge with the facial plate, is devel- 

 oped upon its dorsal surface, * (it is represented in outline in 

 Plate II. Figs. 11 and 12). Connected with the inferior edge of 

 this and almost entirely enclosed within the funnel-shaped 

 integument, a very complicated organ is found ; it is the largest 

 piece in the proboscis, and forms a fulcrum upon which all the 

 other parts move. It gives attachment to five pairs of muscles 

 and guides all the movements of the basal joint, which is other- 

 wise membranous. The walls of this organ are double, and the two 

 plates are kept in apposition by their elasticity, but are capable 

 of being separated and of forming a cavity by the action of a 

 pair of large muscles, the cavity so produced being continuous 



* In order to avoid repetitions, it is to be understood that the words 

 dorral and ventral, as applied to the proboscis, relate to the surfaces which 

 assume those positions when the organ is extended and drawn forward ; 

 anterior and posterior likewise refer to the same position of the organ, 

 that which it would assume if the oesophagus were straight instead of ci;rvcd 

 in the head. 



