THE ORDER DIPTERA 



41 



a tuft, or in a vertical comb, on the pleural plate that lies 

 immediately above the hind legs ; {e) discal — bristles some- 

 times occurring in pairs in the middle of the abdominal 

 terga. 



Alimentary Canal (Fig. 8). — The mouth leads to a 

 muscular pharynx which acts like a suction pump. Connected 

 with the oesophagus there are one or more " crops " or food- 

 reservoirs, the ducts of which may be almost as long as the 

 oesophagus itself. The stomach is large and distensible, its 

 anterior portion, or proventriculus, having a thick, glandular 

 epithelium. The intestine is coiled, and ends in a rectal 

 pouch, which has several (usually four) large glandular 

 papillae on its wall. At the junction of the stomach and 

 intestine the long, coiled Malpighian tubules, which are 



pharynx 



saliv.gland 



Fig. 8.— Alimentary Canal of Mosquito. 



usually four in number, open. The salivary glands are large, 

 and their common duct opens at the tip of the hypopharynx. 



Reproduction. — Most flies lay eggs, which are usually 

 deposited, in a manner that simulates conscious foresight, 

 in a medium or in a pabulum suitable to the future larva : 

 the eggs are large, and are often sticky, so that they cohere 

 in masses. Some flies, such as the flesh-flies {Sarcophaga), 

 give birth to small living larvae ; and there are others, such 

 as Glossina and the Pupipara, that retain and nourish the 

 larva in the oviduct, and do not deliver it until it is full- 

 grown and ready to transform into a pupa. In these last 

 only one full-grown larva is born at a time, but other Diptera 

 produce many eggs (or small maggots) at a birth. 



The larva may be either an eruciform maggot (Lat. 

 eruca = a grub), or may be fairly well endowed. The 

 typical eruciform larva is a segmented worm-like creature 



