184 Annals Entomological Society of America [Vol. XIII, 



great reduction, frequently only an anterior pair and a posterior 

 pair or group remaining. 



The moults seem commonly to be three in number. The 

 exuviae are not as a rule prominent and often are entirely 

 inconspicuous. 



Organs especially adapting the larva to its environment are 

 frequently noted. Curious suckers and pads for clinging to 

 the surface of rocks in swift streams are exhibited by the 

 Simuliidas, Blepharoceridae, etc. Peculiar stellate hairs for 

 increasing surface tension are shown by Anopheles. One of 

 the most interesting structures is the well known "rat-tail" or 

 telescopic, posterior, breathing tube of certain Syrphidae and 

 Ephydridag, which enables its possessor to feed from one to 

 several inches under the water, while breathing air from the 

 surface. 



The majority of dipterous larvae are aerial in respiration; 

 Blepharoceridae and Simuliidas have tracheal or blood gills; 

 while certain Psychodidae have both open spiracles and func- 

 tional gills; and the culicid larvae accomplish respiration in 

 part by spiracles, by gills, through the integument and per 

 rectum. 



Dipterous larv« inhabit well-nigh every accessible haunt 

 on the globe and feed on organic matter in every possible 

 form. 



Many are aquatic — Culicidae, Simuliidae, Blepharoceridae 

 and in part the Tipulidas, Dixidae, Chironomidae, Rhyphidae, 

 Leptidae, Stratiomyidae, Tabanidas, Ephydridse, Sciomyzidae, 

 etc. Some of them prefer the clearest and swiftest of streams, 

 others frequent open still water, some stagnant pools and some 

 the foulest of liquids. In fact, practically every condition of 

 water is utilized by some species of the single family Culicidae. 

 Certain chironomids are said to exist at depths of 1,000 feet. 



The food of these aquatic larvae is very varied and there is 

 a definite correlation between the nature of the food and the 

 specialization of head and mouth parts. Some devour micro- 

 organisms, others small plants, as alg«, others small animals 

 and some doubtless the decaying organic materials them- 

 selves. Many species live in the soil, especially in moist soil 

 or mud. Their food is either other small animals (Tabanidae), 

 or the decaying organic matter which contaminates the mud 

 (Syrphidae), or the roots and tissues of plants (Tipulidae). 



