56 INTERNAL ANATOMY OF INSECTS. 
larva just noticed as having Jour horns, resides under 
the earthy the insect being only aquatic in its grub state. 
2. I am next to consider those respiratory appendages 
by which aquatic insects, since they do not come to the 
surface for that purpose, appear to extract air for respi- 
ration from the water; so that they may be looked upon 
in some degree as analogous to the gills of fishes : there 
is, however, this difference between them — in fishes, the 
blood is conveyed in minute ramifications of the arteries 
to the surface of the branchial laminae, through the mem- 
branes of which they abstract the air combined with the 
water ; but as insects have no circulation, the process in 
them must be different, and their branch iform appen- 
dages may be regarded as presenting some analogy 
rather than any affinity to those of fishes. The first ap- 
proach to this structure is exhibited by the pupa of a 
gnat lately mentioned (Chiro nonius plumosus); for on each 
side of the trunk this animal has a pencil consisting of 
five hairs elegantly feathered, which, when they diverge, 
form a beautiful star ; its anus also is furnished with a 
fan-shaped pencil of diverging hairs a . 
On most of the abdominal segments of the larvae and 
pupae of the Triclioptera are a number of white mem- 
branous floating threads, arranged in bundles, four on 
each segment, two above and two below, and traversed 
longitudinally by several air-vessels or bronchial, which 
run in a serpentine direction, growing more slender as 
they approach the extremity, and in some places send- 
ing forth very fine ramifications, — these are their respi- 
ratory organs b . The caterpillar also of a little aquatic 
a Plate XVI. Fig. 9. a. b. 
h De Geer ii. 539—. t, xi./. 12, 16, &c. 
