3126 THE JOINTED ANIMALS 



and exhibit great dexterity and neatness in piecing them together. The shape of 

 its dwelling, and the nature of the materials used, are often characteristic of the 

 family, sometimes of the genus or species, to which a larva belongs. In the family 

 Phryganeidce , for example, the larvae construct their cases with bits of leaves or 

 twigs, cut into suitable lengths, and arranged side by side in such a manner as to 

 form a spiral band passing many times around the case (see No. 7 in figure). The 

 species of Limnophihis fashion their cases in various styles; the larvae of L.pelluddus 

 using entire leaves, so that the case may have a flattened form, wide in proportion 

 to its depth. The cases made by L. rhombicus consist of bits of sticks or fibres 

 placed transversely, with shells sometimes added; while those of L. flavicornis are 

 often built almost entirely of the shells of different small mollusks, more especially 

 those of Planorbis. What is still more remarkable about these cases is the fact that 

 the casewornfs do not necessarily select empty shells, but take those with living 

 occupants as well, and fasten them all together around their backs. Grains of sand, of 

 finer or coarser kind, are used by many larvae in the construction of their cases; 

 and the latter may be either cylindrical in form or slightly curved, or, as in the 

 exotic genus Helicopsyche, they may, like snail shells, have a distinct spiral cur- 

 vature. The grubs of other species arrange bits of sticks transversely in four 

 different directions, using longer pieces as they progress, so that the complete case 

 is four sided, with the sides gradually widening from one end to the other; and 

 there is a type in which the four sides, instead of being straight, are carried round 

 in a gentle spiral curve. The interior of each larval case is a tubular chamber, 

 lined with silk, open at each end and about wide enough to enable the larva to turn 

 inside. At the fore-end, which is generally a little wider, the head, thorax, and the 

 six legs of the larva may be seen projecting; whereas the hinder end is usually 

 closed by a silken partition pierced with holes. The body of the naked larva is 

 made up of a number of segments, of which the first three carrying the legs 

 are, like the head, hard and of a brownish color; while those that follow, about nine 

 in number, are soft, white, and partly transparent. On the last segment are a pair 

 of horny hooks, which enable the larva to grip tightly to its case. On the first 

 abdominal segment three fleshy protuberances are often seen, a longer one above 

 and a shorter one on each side, which appear to be used in enabling the larva to 

 steady its body in the case, and to regulate its position with regard to the sides, so 

 that the water necessary for breathing may pass freely in and out. The larva 

 breathes by means of rows or tufts of soft white filaments the tracheal gills at- 

 tached to the sides of all the abdominal segments except the first and last, and differ- 

 ing in arrangement in different species. Previously to entering the pupal stage, the 

 larvae of many species provide for their protection during that inactive and helpless 

 period of their existence. They shut themselves up in their cases, some by closing 

 the openings at each end with sieve-like plates of silk, which, while allowing free 

 access to the water necessary for breathing, may serve to keep out their enemies; 

 others by placing stones loosely over the openings, and so accomplishing the same 

 purpose. There are a few larvae, moreover, which, in their earlier days, make cases 

 out of leaves, but add stones as they grow older, until just before pupation begins 

 the case is entirely made of stones. Before the pupa is transformed into the perfect 



