larva twists its body like a corkscrew during the work and weaves an inner 

 layer on both valves. The second half of the case is built by the same 

 method. 



The larva of Orthotrichia tetensii weaves a ring of secretion 

 around the anterior part of its body as a supporting structure and attaches 

 this ring to the filament of an alga (Figure 118). The larva then gradually 

 completes the case with its five dorsal ribs and its weak ventral suture. 



Weaving of nets. The building of primitive tubular nets attached 

 to stones has been little studied. The larva of Wormaldia occipi- 

 talis begins the weaving of its short tubular nets by drawing longitudinal 

 threads and then interweaving them with transverse threads; this is 

 80 reversed when the larva repairs the nets: it first restores the transverse, 

 then the longitudinal threads (Wormaldia, Polycentropus). 



The capturing funnel of Plectorocnemia conspersa is more 

 complicated, forming a large structure, 5 — 10 cm long, in the form of a broad, 

 posteriorly rounded funnel; the opening of the funnel, which is directed 

 against the current, is 4—5 cm wide; the entrance of the net is connected by 

 threads in various directions from the anterior margin to stones or stalks 

 of moss. There is an opening at about the posterior third of the funnel into 

 a tube which is about 5 mm wide and almost as long as the net; almost the 

 whole length of the tube is attached to a hard substrate, e. g., the bottom, 

 stones or stalks of plants; the tube is open, slightly funnel-shaped and 

 loosely attached to plants or stones with several threads; the larva usually 

 remains in the basal part of the tube with its head toward the net; the larva 

 is a predator which catches small and large animals, especially larvae of its 

 own species of almost its own size (Nielsen, 1942:410—412). 



The capturing net of Neureclipsis bimaculata (Polycentropodidae) 

 is very complicated. The building of this net was studied under experimental 

 conditions. The dwelling chamber of the net of a mature larva is not longer 

 (or slightly longer) than the larva; the capturing funnel is very large; in 

 well-developed mature larvae and under favorable conditions it may be 20 cm 

 long, and sometimes even longer (Brickenstein, 1955). 



The dwelling chamber is a simple tube; it is arranged in various 

 directions, depending on the environment; the larva selects a place 

 convenient for attaching the threads which fasten the tube to the substrate; 

 the entrance to the capturing funnel is always directed against the current; 

 the funnel is thus a direct continuation of the dwelling tube (Figure 119, A) 

 or it is coiled once or twice at the base (Figure 119, B, C). 



The building begins from the dwelling chamber; this consists of two 

 activities: finding a suitable place and weaving the tube. The searching 

 activities consist of two types of movements: l) undulating movements, 

 during which the larva remains in its place and moves head and thorax from 

 side to side, examining the surrounding objects; 2) sharp, forward-jumping 

 movements. When it reaches a new place, the larva again makes undulating 

 movements; it places the dwelling chamber in a hollow which is sometimes 

 covered, or in a crack between two surfaces; if there is no better place, 

 it builds the dwelling chamber on a level surface-. The tube is woven by 

 movements of head, legs and body. The larva attaches its threads in various 

 directions, drawing them longitudinally upward or downward (Figure 120); 

 the threads may be of two types: either spun by the spinning glands and 



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