52 INTERNAL ANATOMY OF INSECTS. 



hairs, which are furnished with some repellent material 

 which prevents their becoming wet a : it is this repellent 

 quality that probably causes a dimple or depression of 

 the surface, which if you look narrowly you will discover 

 round the mouth of the tube b . 



When the gnat undergoes its first change and assumes 

 the pupa, instead of a Single respiratory appendage it is 

 furnished with a pair, each in shape resembling a cor- 

 nucopia, and, what is remarkable, placed near the oppo- 

 site extremity of the body, for they proceed from the up- 

 per side of the trunk c . By these tubular horns, which 

 Reaumur compares to asses' ears d , they respire, and are 

 suspended at the surface. 



Other respiratory tubes or horns are more complex. 

 The rat-tailed grub of a fly (Helophilus pendulus), like 

 the gnat, breathes by^a tube : but as if the CREATOR 

 willed to show those whose delight it is to investigate 

 his works, by how many varying processes he can ac- 

 complish the same end, this respiratory organ is of a 

 construction totally different from that we have been 

 considering. It is not fixed to the side of the tail, but 

 is a continuation of the tail itself, and is composed of two 

 tubes, the inner one, like the tube of a telescope, being 

 retractile within the other e . The extremity, which is 

 very slender, and through which the air finds admission 

 by a pair of spiracles, terminates in five diverging hairs 

 or rays, which probably maintain it in equilibria at its 

 station at the surface f . As these larvae seek their food 



a PLATE XIX. FIG. 9. b. 



h Compare Swamm. Bibl. Nat. i. 154. t. xxxi./. 5. Reaum. iv. 

 601. t. xliii. De Geer vi. 317. t. xvii./. 28. 

 c Swamm. Ibid. t. xxxi./. 7, 8. d Reaum. iv. 007. 

 e PLATE XIX. FIG. 12. a. f Reaum. iv. t. xxxii./ 2. e. 



