22 THE EARLY STAGES OF rABANIDE 



by the contractions of the muscle fibers in the wall. The mid gut 

 is, at least in the species studied by Patton and Cragg, of a strik- 

 ing orange-red color in the fresh condition, and is filled with a semi- 

 solid mass of a light chocolate color, which oozes out if the wall is 

 punctured in dissecting. The hind gut is short and simple, and is 

 coiled up in the posterior end of the abdomen. The total length 

 of the gut is about twice the length of the body of the larva. The 

 salivary glands are simple and tubular, and bear a remarkable resem- 

 blance to those of the adult insect. 



Respiratory System. — The respiratory system resembles that of the 

 mosquito larva. There are two large lateral tracheae which run the 

 whole length of the body on each side of, and slightly dorsal to the 

 alimentary canal. According to Patton and Cragg (1913), these 

 communicate with the external air through an opening, which can be 

 closed, on a small prominence on the dorsal surface of the penultimate 

 segment. This statement appears to be erroneous. Brauer (1883) 

 states that the tabanid larvae are usually metapneustic, the last 

 segment with a vertical respiratory fissure or the last two segments 

 forming a respiratory tube. According to Malloch (1917), they are 

 always metapneustic. The respiratory tube is of varying length, 

 sometimes very short, sometimes more slender and tube-like, or form- 

 ing a short acute spine. The two main air-filled trunks are much in- 

 flated in some species, enabling the larvae to float at the surface of 

 the water, and narrow, almost filiform in other species. As they pass 

 forward, they give off slender branches of tracheae to the body cavity 

 in each segment. In the anterior part of the body the tracheal 

 stems, in the species where they are generally much inflated, become 

 slender, describing one or several semicircular loops and tapering into 

 fine tracheae going to various organs. The tracheal branches going 

 to the body wall of each segment may be homologous with those 

 leading to the abdominal spiracles in amphipneustic larvae. 



Dorsal Blood Vessel. — The dorsal blood vessel is easily seen in trans- 

 parent larvae and ends blind, in the cases observed, before the elev- 

 enth segment. 



Malpighian Tubes. — The Malpighian tubes are, to judge from 

 Patton and Cragg's figures, four in number, in young larvae irregu- 

 larly crowded in the posterior part of the body between the two 

 tracheal trunks, and of brownish, greenish, or yellow color. 



