INTERNAL ANATOMY OF INSECTS. 55 
other gnat Reaumur discovered Jour a . The larva of 
Tanypus maculatus, whose remarkable legs I formerly 
noticed b , exhibits in the interior of its trunk two long, 
oval, opaque bodies, which De Geer conjectures may be 
air-reservoirs ; these, when the animal assumes the pupa, 
according to every appearance become external, and are 
placed on the back, precisely where the respiratory 
horns of aquatic pupse are usually situated, — they appear 
to terminate in a transparent point c . The pupa of a 
Tipula observed by Reaumur, instead of two has only 
one of these respiratory organs, in the form of a very 
fine hair proceeding fi-om the anterior end of the trunk, 
and considerably longer than the animal itself d . 
It is observable that aquatic insects that come to the 
surface of the water for air, receive it at the anus, often 
carrying it down with them as a brilliant bubble of quick- 
silver. This is generally done by means of spiracles in 
perfect insects, but in the water-scorpion tribe in that 
state respiration is by means of a long hollow tube, con- 
sisting of two concavo-convex pieces which apply exactly 
to each other. This is found in both sexes, and there- 
fore cannot be an ovipositor, as some have thought e . 
These respiratory organs, however, are not invariably 
confined to aquatic larvae and pupae, for those of some 
aphidivorous flies have anal ones, and the pupa of Doli- 
chopus nobilitatus, or a fly nearly related to it, which is 
terrestrial, has likewise a pair of long sigmoidal ones on 
the back of the trunk f . The pupa also of the rat-tailed 
* Reaum. v. t. W.f. 6. s, u. b Vol. II. p. 275—. 
c De Geer vi. 395—. t. xxiv./. 16. 18. d. d v. t. vi./. 1, 2. 
' De Geeriii. 367. t. win./ 1, 2, 9. 
' Ibid. vi. 36. 194—. /. ii./. 2, 3. s. 
