303 



a pair of closely fused pseudopods ; thoracic segments slightly swollen; 

 apical 3-4 segments of abdomen much swollen, giving the larva a 

 slightly club-shaped appearance ; apical segment with a sucker-like disc 

 which is armed with a number of stout, short, hook-like bristles ar- 

 ranged in concentric series. 



Pupa (PI. XLV, Fig. 9; PI. XLVI, Figs. 2, 3).— Head without 

 projecting spines; palpi directed caudad; thoracic respiratory organs 

 each consisting of 4 to 60 tube-like filaments ; legs extending but little 

 beyond apices of wings ; abdomen armed with short spines on apices 

 of segments. The pupae are enclosed in a slipper-shaped or pocket- 

 like cocoon (PI. XLVI, Fig. 4) or occasionally in a tangled mass of 

 loose threads. 



Imago. — Antennae ii-jointed, the joints of the flagellum short 

 and rather closely attached. Eyes of male confluent, with the facets 

 of the upper half much larger than those of the lower half (PI. XLVI, 

 Fig.- 5) ; eyes of female rather Widely separated, the facets of nearly 

 uniform size throughout. Wings without cross-veins in the disc; 

 radius with 2 or 3 branches. Abdomen with 7-8 segments, and a flap- 

 like scale at base the apex of which is fringed with long soft hairs. 

 Legs stout; metatarsus very long and stout; claws trifid in male, 

 bifid or simple in female. 



HABITS OF IvARVAE 



The known larvae of the species of this family are aquatic, invari- 

 ably living in water that is in motion, never occurring in ponds or 

 stagnant water. Removal to still water in vials or other vessels re- 

 sults in the death of the specimens in a few hours. The food of the 

 larvae consists of diatoms, algae, and other minute organisms. When 

 disturbed in the streams in which they occur the larvae usually release 

 their hold upon the surface of the rock, or other object in the bed of 

 the stream, and float off to some distance, maintaining slight attach- 

 ment, however, by means of a silken thread which emanates from the 

 mouth. When the danger has passed they regain their former hold 

 in the bed of the stream by means of this thread. Their method of 

 locomotion reminds one forcibly of that of the geometrid moths, con- 

 sisting of a series of looping movements, interrupted by frequent 

 pauses during which the head and the anterior portion of the body are 

 moved restlessly from side to side as if the insect were looking for 

 something. Most species hibernate in the larval stage, appearing as 

 imagines in spring and early summer. A few species have evidently 

 more than one brood in the year. 



