conditions of movements in different groups. The claws also vary accordingly; 

 they may be large or small, long and narrow, laterally compressed or short, 

 and expanded at the base. The curvature of the claw and the breadth of its 

 membranous part are also very variable; the arrangement and relative 

 length of the setae of the claw also vary; some of them increase, others 

 decrease in size, becoming thin and hardly noticeable; The anal legs of the 

 larvae of some species of Rhyacophila are an example of complex 

 structure; part "a" is absent (Figure 193), and the massive and broad 

 29 part "b" occupies the larger part of the leg; the large dorsolateral sclerite 

 of this part bears a thick black ventral hook on the outer side, near the base; 

 near the hook is a small ventral plate bearing a seta (this plate is separated 

 from the sclerite); there is an upward directed, blunt tubercle dorso- 

 distally at the base of which are pits articulating with the claw on each side; 

 on the outer side is a long posteriorly directed, sword- shaped lateral 

 process. Part "c" bears two small sclerites with a small seta on the 

 smaller sclerite. The ventral side of the curved claw with its large basal 

 part bears three tubercles near its suture; one in the basal part and two in 

 the apical part. Seta 3 is displaced to the dorsal side; the ventral setae 7 

 and 8 are curved, light-colored and relatively thick. 



Tracheal gills. The tracheal gills of the larvae of caddis flies are 

 outgrowths of the integument with a tracheal trunk inside the body; this trunk 

 is branched toward the surface of the gill, and each cell of the respiratory 

 epithelium of the gill is surrounded by tracheoles. 



FIGURES 16-19. Tracheal gills: 



16 - Rhyacophila nubila; 17 - Phryga ne a striata, segments 7 and 8; 18-Limno- 

 philus rhombicus; 19 - Odontoc erum albicorne (after Nielsen). 



25 



