56 INTERNAL ANATOMY" OF INSECTS. 



larva just noticed as having four horns, resides under 

 the earth) 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 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 (Chironomusplumosus); 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 Trichoptera 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 bronchia, 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. 



b De Geer ii. 539. t. xi./. 12, 16, &c. 



