54? INTERNAL ANATOMY OF INSECTS. 



other instances, proceed to the end, and terminate in 

 the two spiracles mentioned above : he conjectures that 

 when the animal has occasion to push forth its respira- 

 tory apparatus, it injects into these vessels part of the air 

 contained in the body of the trachea^ which of course 

 would cause them to unfold and push forth the tube a . 

 When this insect assumes the pupa, instead of its anal 

 respiratory organ it has four respiratory horns in the 

 trunk near the head b . 



The larva of the chamaeleon-fly (Stratyomis ChamcE- 

 leori) is furnished with a respiratory organ of a still dif- 

 ferent and more elegant structure, exhibiting some re- 

 semblance to the tentacula of what are called sea ane- 

 monies. In this larva the last joint of the body is ex- 

 tremely long, and terminates in an orifice to receive the 

 air, which is surrounded by a circle of about thirty di- 

 verging rays, consisting of beautifully feathered hairs or 

 plumes c . This apparatus serves the same purpose with 

 that above described of the larva of the gnat. The fea- 

 thery hairs are so prepared as to repel the water, and 

 thus to suspend the animal by its tail at the surface, and 

 preserve a constant access of air. When it has occasion 

 to sink, it turns these hairs in and shuts the orifice, 

 carrying down with it an air-bubble that shines like 

 quicksilver, and which Swammerdam conjectures enables 

 it again to become buoyant when it wants to breathe d . 



In the red aquatic larva of a small gnat (Chironomus 

 plumosus) there are two anal respiratory subcylindrical 

 horns, with the orifice fringed with hairs e ; and in an- 



a Reaum. iv. t. xxx./. 447. b Ibid. 45fi. t. xxxi./. 17. 



c PLATE XtX. FIG. 13. c. d Bibl. Nat. ii. 44. 



e PLATE XIX. FIG. 10. a. 



