INTERNAL ANATOMY OF INSECTS. 55 



other gnat Reaumur discovered four 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 pupae 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 from 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. iv./. 6. s, it. b VOL. II. p. 275. 



De Geer vi. 395. t. xxiv./. 16. 18. d. d v. t. vi./. 1, 2. 

 De Geer iii. 367. t. xviii./. 1, 2, 9. 

 Ibid. vi. 36. 194. t. ii./, 2, 3. s. 



