THE ANIMAL KINGDOM. 117 



admiration. The extraordinary tail to which the animal 

 owes its name is an organ of respiration. It contains two 

 vessels which serve to disseminate the air through all the 

 body of this fly-larva, for such it is. These two air-chan- 

 nels are enveloped by tubes of a different calibre, which fit 

 one into another and move exactly like the tubes of a tel- 

 escope. 



This worm, not having any swimming organ, possesses in 

 this ingenious arrangement a means of constantly opening 

 the orifice of its respiratory apparatus at the surface of the 

 water, whatever may be its level. If the liquid sink in the 

 puddle which it inhabits, all the tubes enter one another 

 like those of a telescope, and the aerial tubes wind inside 

 them. If, on the contrary, a violent shower should make 

 the water rise above its bounds, they are all projected out- 

 wards, being drawn out as far as possible, so that their ori- 

 fices still reach the surface. 



The final intention of nature is so manifest in this cir- 

 cumstance that if we, in imitation of Reaumur, plunge one 

 of these larvfe into a glass containing only a little water, 

 and the quantity of this be gradually augmented, the in- 

 sect's tail lengthens in proportion, and indeed acquires an 

 extraordinary size, so that, without quitting the spot, the 

 larva may carry on the act of respiration, the aerial tubes 

 opening out on the surface of the fluid. 



The ravages of insects, which sometimes occasion such 

 serious panics, are explained by their enormous fecundity. 

 This is sometimes so prodigious that some persons imagine 

 it results from a sudden creation en masse. On this sub- 

 ject Leuwenhoeck calculated that a single domestic fly can 



