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FIGURE 111. Building of the case by 

 the larva ofPhryganea grandis: 

 case of a young larva (A), anterior 

 margin of the case during adding pro- 

 cess (B) (after Wesenberg-Lund) 



many species are positively phototropic (Triaenodes bicolor). The 

 main object of the larva after leaving the egg is to cover itself as rapidly 

 as possible with a tube; the larva may then begin to feed and perfect the 



case. The first case is called a "temporary 

 ... : ^ ; ,. case"; it is a primitive structure which, as 



the larva grows, is gradually replaced by the 

 strongly built definitive case, having the 

 distinctive characteristics of the species. 

 When a mature larva is deprived of its 

 case, it rapidly builds a temporary one; 

 under its protection it thus adds to the case, 

 and restores the lost one; however, the new 

 structure is usually less perfect than the 

 original one. 



We describe below the building of tubes 

 of several species which use plants, detritus, 

 sand or secretion without an outer layer. 



When the larvae of the large species of 

 Phryganea (Ph. striata, Ph. grandis) 

 hatch from the egg (Figure 80, A), they 

 rapidly cover themselves with their temporary 

 case which consists of detritus glued together 

 with silk. The larvae of Ph. striata find material for their first case 

 either on the egg mass or collect it among the vegetation which is always 

 more or less covered with fine detritus. Before building the case, or while 

 they bear the temporary case, the small larvae of Phryganea 

 (Figure 80, B) are suspended in water, making clumsy swimming movements 

 and bending the abdomen; this ability is lost as the temporary case becomes 

 thicker. 



The larva then bites off thin fragments, arranging them so that their end 

 remains free and the case assumes a shaggy appearance; the spiral 

 arrangement of the particles in the structures of young larvae may be 

 weakly marked but becomes better established later (Figure 11, A, B). In 

 the older stages, when the regular spiral has been built, the larva 

 (Ph. grandis) weaves a net in the corner formed by the last glued bit and 

 the anterior margin of the case; the larva thus adds an internal sheath to 

 the case. When the silk net is ready for the addition of the outer layer, it 

 takes a small fragment of a plant leaf; it "licks" one side of the fragment 

 with its labium, smearing it with the secretion of the spinning glands; the 

 leaf fragment is thus placed so that its sticky side touches the woven part 

 of the internal sheath; the larva then alternately touches the new fragment 

 and the adjacent one with its labium and connects the fragments with a 

 zigzag seam. The whole process takes about one minute or slightly longer. 



The larvae can repair the case. If a part of the case of the larva of 

 Phryganea grandis is cut off, the larva can reconstruct a long part of 

 the tube in one night (Wesenberg-Lund, 1911b:78— 85). 



When the larvae of Phryganeidae, which live in tubes with a posterior 

 opening are removed from the case, they return to it and assume their 

 initial position; larvae of Agrypnia pagetana Curt, forced to leave 

 the case return to it rapidly and repeatedly. 



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