remain directed forward (e. g., in the genus Agapetus)) the setae of the 

 middle and posterior areas are displaced toward the peri-ocular setae, 

 forming one group together with them (see Figure 3 70). In larvae whose 

 eyes are displaced far posteriorly (e. g., the genus Silo), some of the 

 setae of the anterior part are displaced posteriorly together with the eyes, 

 and only setae 7 and 8 retain their position at the base of the mandibles. 

 In free-living larvae with a long prognathous head, the setae of the anterior 

 17 part of the head are well developed, while the setae of the posterior part are 

 short (Rhy ac ophil a, Wormaldia, Po ly c e nt r o p u s). In case-bearing 

 larvae with a hypognathous head, in which the dorsal process of the anterior 

 margin overhangs the opening of the case, the setae of the anterior and 

 posterior part are uniformly developed: seta 15 is thin, about as long as 

 seta 14 (Limnophilidae); seta 17 is thick and one of the longest setae of the 

 head (Brachycentridae). 



The mouthparts of the larvae of caddis flies are of the biting type and 

 are well developed; the movable labrum (Figure 5) covers the preoral 

 cavity from above: the mandibles have a grasping function, bite the food 

 and chew it; they break and form the material used for the building of the 

 case; the maxillae and labium take part in the capture and retention of the 

 food and pass it into the mouth through the preoral cavity; they also act as 

 spinning organs. The mandibles are short, massive and strongly sclerotized 

 the maxillae and labium are oblong, more or less soft structures which 

 consist mainly of membranous integument which bears small sclerites. The 

 differences in feeding methods and building activity results in marked 

 morphological differences in the mouthparts. 



The mandibles are of the biting or scraping type (Figure 6); they are 

 short, massive, with a triangular base and irregular surface: the outer 

 surface is curved, the ventral surface more or less flattened or convex 

 and the dorsal surface concave; the distal end of the mandible is pointed. 

 The mandibles are articulated with the parietal sclerites at the corners 

 of the outer side of the base, by an acetabular-condylar articulation; the 

 dorsal articular process bears an acetabular pit at the apex, the ventral 

 articular process bears a condylar head which is connected with the 

 mandible by a short neck; the situation is the opposite at the parts of the cranium 

 articulating with the mandible: the condyle is situated dorsally and the 

 acetabulum ventrally. The tendon of the strong adductor muscle originating 

 at the posterior wall of the cranium and filling the greater part of its cavity 

 is attached to the inner angle of the base of the mandible. The outer 

 margin of the base of the mandible is always convex; the tendon of the 

 abductor muscle originates at the apex of the arch. The inner concave 

 margin of the mandible forms two cutting edges: the upper and lower blade 

 (Figure 6); both blades are more or less equally developed in some predators 

 (Polycentropodidae); in others, the upper blade is displaced toward the outer 

 margin and forms a ridge (Hydropsychidae); the upper blade is sometimes 

 reduced and the blades are flat and knifelike. The distal part of the upper 

 and lower blade usually bears 2 or 3, rarely 1—4 pointed or blunt teeth; the 

 tip of the mandible is pointed, and forms a long or blunt and broad tooth; 

 there is a large basal masticatory tooth in some forms. The teeth of 

 phytophagous forms are not situated on the blades but on the distal, broad 

 margin of the mandibles. In forms living on epiphytic algae, the distal 

 part of the mandible is without teeth, and the mandibles are spatulate, 



14 



