ENEMIES OF APHIDES. 39 



anatomy of which the Syrphidse nearly approach — the organ con- 

 sists of three joints, corresponding to, or rather modifications of, 

 the three anterior segments — a^ b, c. The foremost, ^, consists of 

 a pair of membranous lobes of somewhat triangular shape, each 

 of which is divided, on its outer side, about the^ middle of its 

 length by a deep cleft. Each lobe is provided with a series of 

 channels, known as "pseudo," or "false tracheae," and consisting 

 of a number of parallel membranous grooves, to which a vast 

 number of incomplete rings give a semblance of tracheae. These 

 channels arise posteriorly from a transverse channel of similar 

 structure, larger in size, and placed at only a slight obliquity to 

 the central line of the proboscis. 



Each lobe is supported by a curved chitinous arm, taking its 

 rise in the mass of muscles at the base of the second or middle 

 joint, and between these supports a pair of oblong chitinous plates 

 attached one to either lobe, from the extremity of the longitudinal 

 hollow on the upper side of the second joint, in which the ligida 

 (d), labium fej, and maxillce. f/, f) lie concealed. 



The second joint (b) consists of two more or less substantial 

 chitinous processes, which support the muscles on the ventral 

 aspect, and between which, on the dorsal surface, is the channel 

 above mentioned for the reception of the tongue and its append- 

 ages. These are attached by membranous and tendonous connec- 

 tions at the base of the second segment, the apodemes of the 

 maxillae extending to the ventral side of the pharynx in the third 

 or basal joint. 



The slender, acute, chitinous tongue, d^ forms with the labium, 

 ^, which is furnished at its extremity with several comb-like pro- 

 cesses, a hollow tube, which is continuous posteriorly with the 

 pharynx, and which receives and passes on the food obtained by 

 the suctorial lobes. This will be further referred to in the next 

 section, when the food will be considered. Near the extremity of 

 the tongue is the opening of the salivary duct, which, arising; from 

 the salivary glands, is continued through the strong, triangular 

 chitinous structure, n^ of the third joint, which encloses the 

 pharynx. The second joint and the suctorial lobes are amply 

 supplied with the necessary air by extensions of the delicate 

 tracheal sac, composed of a crape-like membrane, and situated on 



