INSECTS. 
157 
forms of month are but modifications of the same model, 
adapting it to different functions. The sheath, horny and 
tubular in the Gnat, soft and muscular in the Fly, is the 
lower lip ; the piercing lancets in the former are the jaws, 
which are inconspicuous in the latter. The elegant coiled 
spire of the Butterfly consists of two tubes, which are the 
lower jaws, greatly lengthened; and the labial palpi, 
stout and hairy, stand up on each side of them : the other 
essential parts can be detected only by the skill of the 
anatomist. 
Some of the most interesting of the phenomena which 
occur in the economy of Insects, arc the transformations 
which they exhibit ill their progress of growth ; the 
changes of their form being frequently so great, that it 
would be impossible, but for the testimony of experience, 
to avoid the conclusion that the same insect, in infancy, 
youth, and adult age, belonged to widely distinct and re- 
mote orders of existence. We shall enter into some 
details of this interesting subject in our next chapter. 
