TRICHOPTERA. —— PHRYGANEIDE. 63 
same manner as caterpillars. Some cases are formed of fine sand, and 
curved ( fig. 68. 4. case of Sericostoma multiguttatum Pietet). The 
Jarva remains in this case, exposing only its head and three anterior 
segments of the body, and which it suddenly withdraws on the 
slightest alarm. 
The eases formed by these larvee being ordinarily composed of mate- 
rials scarcely specifically heavier than the water, are easily carried 
about. There does not appear to be an exclusive regularity in the choice 
of the materials of which they are formed, according to the difference of 
species, the individuals of each employing, occasionally, what comes 
nearest to them when engaged in its construction. M. Pictet indeed 
appears to consider that each species chooses its own peculiar materials 
for the construction of its case, and that the mode in which these 
articles are applied is uniform. Thus, P. rhombica selects morsels of 
straws or twigs, which it arranges transversely (fig.68.1.); whilst P. 
lunaris employs the same materials, which it attaches longitudinally 
( fig. 68.3.). He, however, mentions a variety of instances in which 
materials of a perfectly different kind had been employed by these 
species. In some species, the materials (ordinarily strips of leaves) 
are arranged in a spiral coil (fig.68.9. pupa case of P. varia Pict. 
Reaum. 3. pl. 14. f.9.). 
When the case, owing to the growth of the inhabitant, becomes too 
small, it has been stated by some authors that the larva quits it and 
constructs a new one; but M. Pictet considers that it rather adds fresh 
materials of an enlarged diameter at the aperture, cutting off a por- 
tion of the opposite end, which would account for the conical form 
which these cases often exhibit. 
In the preface to the Historia Insectorum of Ray, p. xii., is pub- 
lished an interesting tabular arrangement of these cases, ‘‘ ex obser- 
vatione D. Willughby,” of which an extract will be sufficient to prove 
the assiduous but neglected researches of our celebrated countryman. 
*“‘ Insecta aquatica thecis se contegentia sunt, vel theca 
immobili, seu lapidibus affixa, corpore vel 
subrotundato cum filamentis ad latera, 
plano et compressiore absque filamentis. 
mobili aut portatili, migratoria; Phryganea vulgo dicta. [Then 
follows an admirable description of the larve inhabiting these 
moveable cases.] Suntque vel thecis 
rectis, vel habentibus 
festucas agglutinatas 
