40 PREDACIOUS AND PARASITIC 



the ventral side of the basal joint. Arising from the thickened 

 folds at the base of the maxillae, and belonging to the basal rather 

 than the intermediate joint, are a pair of labial palpi, g, presenting 

 a somewhat lanceolate appearance in Eristalis^ but in Syrphus 

 more club-shaj^ed, and resembling the same organs in the Mus- 

 cidce. They are covered closely with minute bristles and sparsely 

 with longer hairs, one or two of especial length and size arising 

 from the apex. 



The third or basal joint, <:, consists of the folds of integument 

 surrounding the triangular chitinous structure forming the founda- 

 tion of the whole proboscis. These folds are continuous with the 

 integument of the fourth or antennal segment, which is in imme- 

 diate proximity to the facial opening, in which the proboscis lies 

 hidden when at rest. This segment contains the muscular 

 apparatus by which the chief movements of the proboscis are 

 accomplished, consisting mainly of five pairs of muscles attached 

 to the above-mentioned chitinous framework. It also contains the 

 tracheal sacs, or air reservoirs supplying the organ, and gives 

 passage to the prolongations of the cephalic ganglion which inner- 

 vate the muscular system. The triangular framework of chitin, //, 

 consists of a pair of thin plates, thickening on their ventral edges 

 to solid ridges, between which passes the pharyngeal tube. The 

 whole structure is anchored by means of two projecting processes, 

 or apodemes, in oval muscular masses, and between them issues the 

 continuation of the pharyngeal tube forming the oesophagus (i, i). 



The oesophagus consists of an extended narrow tube, which, 

 bending sharply at its commencement, pierces the cephalic 

 ganglion, and ends in an enlargement just above the proventricu. 

 lus or gizzard (;//), where are situated the muscular valves control- 

 ling the passages to the sucking stomach or crop {k) and to the 

 digestive stomach (I) respectively, y 



The appearance of the oesophagus, when viewed in dilute 

 glycerine under a ^-in. objective, is sufficiently remarkable. The 

 internal surface is covered with bristles, somewhat irregularly 

 placed and generally pointing downwards. These take their rise 

 in the third or membranous coat, which is insoluble in potash, 

 and is continuous with that of the pharynx and the proboscis. 

 The two outer coats of the oesophagus consist of circular and 



