336 NKW YORK STATE MUSEUM 



free, when suddenly they spread out fanlike and held above 

 the surface of the shallow water, the legs all bunched up and 

 still remaining in the pupal skin. The force of the flowing- 

 water and the struggles of the insect in from one to five minutes- 

 cause the legs to draw out^ and, thus liberated, the imago im- 

 mediately takes flight. In deeper water the wings probably do 

 not unfold till after the insect is washed to the surface, though 

 no observations were made upon this. Figures of larvae and 

 pupae may be found in Oomstock's ManiMl, and in Kellogg's 

 papers in the Entomological News for 1900, and in Cal. Ac. Soc. 

 Proc. 1903. 



Family sirviuLiiDAB 

 BlacJc flies 



In this family the body is short and stout; the legs are short; • 

 and the tibiae possess spurs. The antennae are scarcely longer 

 than the head, cylindric and 10 jointed; the two basal joints are 

 differentiated; the others are closely united. Proboscis not 

 elongated, with small horny labella; palpi are four jointed. The 

 thorax is much arched, giving the fly a humpbacked appearance ; 

 the scutellum is small; the abdomen is cylindric, composed of 

 seven or eight segments; the legs strong and not elongate. The 

 wings are broad, iridescent, and not clothed with hairs. The 

 veins near the costal border are stout; those on the other parts 

 of the wing are very weak, [^ee pl.34, fig. 1] 



The larvae are soft skinned, not slender, usually more or less 

 constricted in the middle. The head is cylindric, with eye spots 

 on each side. The head bears two large fan-shaped organs, 

 which aid in procuring the food. Respiration is accomplished 

 by means of three blood gills which are pushed out from the 

 dorsal surface of the last abdominal segment (Miall & Ham- 

 mond say from the rectum). On the segment back of the 

 head is a foot armed with hooks, and on the posterior 

 end of the body is a disklike sucker by means of which the 

 larva clings to the rocks or to plants. The creature moves 

 about on the surface of the rocks with a looping gait similar 

 to that of a measuring worm, and a web is secreted which pre- 

 vents its being washed away ^>^ +^f swiftlv flowinp- water. 



