THE ANIMAL KINGDOM. 



129 



for such it is. These two aerial canals are enveloped by 

 tubes of a different calibre, which fit one into another and 

 move exactly like the tubes of a telescope. 



75. Common Gnat, CuJcx pipiens, and its Metamorphoses, magnified. Larvae opening tlieir 

 Eespiratury Doors on tlie surface of the water. Nymplis and Perfect Insects. 



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 



17 



