68 MODERN CLASSIFICATION OF INSECTS. 
table, confirming, in respect to the peculiarities in the preparatory 
states, the genera founded upon the characters of the imago. 
(a ( ( External organs of respiration ; 
Thoracic | .. lated, legs moderate oi eaten: 
Larvee with Rt SA 3 External 
enclosed a 2 organs of Hind legs long - Mystacida. 
respiration legs short - Sericostoma. 

: 2 rounded. 
ina <_ circular | 

moveable | opening. Lin bundles. 
case Thoracic segments with the front angles Trichestora: 
pointed - - - 
Lopening with a slit - - - Hydroptila. 
Larve not 
enclosed { The pupa enclosed in a double envelope - - Rhyacophila. 
ina move- { The pupa enclosed ina single envelope - - Hydropsyche. 
able case. 
M. V. Audouin has shown me the case of a small unknown species 
of this family, quite unlike any hitherto figured, being composed of 
fine sand cemented together, and saucer-shaped, so that it is difficult to 
conceive how the larva could employ it as a means of defence or abode. 
When the period for assuming the pupa state is arrived, the larve, 
which reside in moveable cases, fasten them to some fixed substance 
beneath the water, and close the two extremities with an openwork 
fence, which varies in form in the different species, and which, by admit- 
ting a current of water, permits the respiration of the pupa; indeed, 
Reaumur states, that he actually saw this gratework in alternate 
motion from convex to concave, as the water passed out and in ( fig. 
67. 12. represents the grating of the case of P. fusca? after De Geer). 
Within this retreat they then became inactive pupa, in which they 
bear a considerable resemblance to the imago, except that the an- 
tenne, palpi, wings, and legs are shorter, enclosed in separate sheaths, 
and arranged upon the breast (fig. 67.13. pupa of P. pellucida De 
Geer), the antennz, in the species which have those organs, greatly 
exceeding the length of the body, being extended beyond the abdomen, 
with the extremities curled up ( fig. 67. 17. pupa of Mystacida bimacu- 
lata De G'eer). The front of the head ( fig. 67. 14. head of pupa of 
Hydropsyche senex Pictet) is moreover furnished with a pair of cor- 
neous hooks, but which are the real mandibles, crossing each other, 
and different in form from those of the larva and pupa, which give 
the head the appearance of a beak, varying in form and strength in 
the different groups, according to the nature of the cocoons (fig. 
67.15. mandible of pupa of Hydropsyche atomaria Pictet). With 
this the pupa makes its way through the openwork mouth of its 
case, shortly before assuming the perfect state, at which period it 
