NEUROPTERA. 
161 
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 Pkryganeidce, 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 Limnophilus fashion their cases in various styles; the 
larvae of L. pellucidus 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. fiavicornis are often built almost entirely of the shells of different small 
molluscs, more especially those of Planorbis. What is still more remarkable about 
these cases is the fact that the case-worms 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 curvature. 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 colour ; 
while those that follow, about nine in number, are soft, white, and partly trans¬ 
parent. 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—attached to 
the sides of all the abdominal segments except the first and last, and differing 
in arrangement in different species. Previously to entering the pupal stage, the 
larvae of many species provide for their protection during that inactive and help¬ 
less 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 insect, it extricates itself from its case, and leads an active life, swimming 
VOL. VI.—II 
