56 INTERNAL ANATOMY OF INSECTS. 
blood is conveyed in minute ramifications of the arteries 
to the surface of the branchial laminze, through the mem- 
branes of which they abstract the air combined with fhe 
water; but as insects have no circulation, the process in 
them must be different, and their branchiform 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 (Chironomus 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*. 
On most of the abdominal segments of the larvee and 
pup of the Trichoptera (Phryganea L.) are a number 
of white membranous floating threads, arranged in bun- 
dles, four on each segment, two above and two below, 
and traversed longitudinally by several air-vessels or 
bronchia, which run in a serpentine direction, growing 
more slender as they approach the extremity, and in some 
places sending forth very fine ramifications,—these are 
their respiratory organs». ‘The caterpillar also of a little 
aquatic moth (Botys stratiotalis) at first sight appears to 
be covered on each side with hairs, but which examined 
under a microscope are found to be branching flattish 
filaments, each furnished with tubes from the trachee. 
These caterpillars have also the semblance of spiracles, 
but apparently found in the usual situation®. The larva 
of a little beetle often mentioned in my letters (Gyrinus 
@ Pirate XVI. Fic. 9... 8. 
> De Geer ii. 539—. t. xi. f. 12, 16, &c. 
© Ibid. i. 526—. 4. xxxvii. f. 2—6. 
