3G THE MAGGOT OF 



be apparent that the contraction of the muscles in.m. will withdraw 

 the superior wall of the oesophagus from the inferior wall, thus 

 enlarging its capacity and producing an inflow of the fluid aliment 

 upon which the fly feeds ; the tissues of the meat having been 

 reduced to this semi-fluid condition by the tearing process of the 

 mandibles, aided probably by the solvent action of the salivary 

 secretion poured out for the purpose. The approximation of the 

 pharyngeal walls to their former condition, and the further 

 propulsion of the food into the oesphagus and crop is probably 

 effected by the external muscles. In front of the pharynx there 

 are two or three small pieces terminating in the mandibles, to the 

 base of which powerful muscles are attached, and by which their 

 movements are effected, as recently shown, I think, by the Rev. 

 J. H. Green, in a sHde circulated by him. Beneath the mouth a 

 small fleshy conical labium may be perceived. 



In all insects a web of fibrous and fatty tissue intervenes 

 between the alimentary canal and the body-wall. A portion of 

 this fatty rete is shown in Fig. lo, the cells are about i-3ooth of an 

 inch in diameter and are filled with oil globules and granules, which 

 render them white by reflected, and dark by transmitted light. 



The tracheal system of this larva is a very favourable subject 

 for study, the tracheae showing out silvery white by reflected light, 

 so that all their ramifications are visible. Two main branches 

 extend from the posterior spiracles the whole length of the body, 

 their ultimate ramifications extending around the sensory-ganglia 

 in the front of the head ; a strong transverse branch connects 

 them close to their origin in the thirteenth segment, and another 

 near the head in the third segment. In every segment branches 

 proceed from these main trunks, some of which anastomose with 

 each other in the central line, while others proceed to the 

 muscular, nervous, and digestive system (as seen in Fig. it). 



The tracheae consist of two coats : an inner coat, corresponding 

 to the outer layer of the integument, of which it is the continua- 

 tion, and an outer epithelial coat corresponding to, and continuous 

 with, the inner epithelial lining of the integument (see Fig. 12). 

 The spiracles in the mature larva are four in number — two in the 

 last segment, placed in the centre of a circlet of blunt, conical 

 processes which terminate the body, and two in the second seg- 



