302 THE MECHANICAL FUNCTIONS. 



Nature has farther provided insects with in- 

 struments adapted to different kinds of external 

 actions. They consist of articulated levers, va- 

 riously combined together, and forming legs, 

 claws, pincers, oars, palpi, and, lastly, wings, 

 calculated for executing every variety of prehen- 

 sion, of progression, or whatever other action 

 their wants and necessities require. 



3. Developement of Insects. 



IT would appear as if the final accomplishment 

 of objects so numerous, so widely different, 

 and so liable to mutual interference, could be at- 

 tained only by the animal being subjected to a 

 long series of modifications, and passing through 

 many intermediate stages of developement. The 

 power of flight is never conferred upon the in- 

 sect in the earlier periods of its existence : for 

 before its structure can obtain the lightness 

 which fits it for rising in the air, and before it 

 can acquire instruments capable of acting upon 

 so light an element, it has to go through several 

 preparatory changes, some of which are so con- 

 siderable as to justify the term of metamorphoses, 

 which has been generally given to them.* But 



* Transformations quite as remarkable occur in several tribes 

 of animals belonging to other classes : such as those of the Frog 

 among reptiles, and of the Lerncea among parasitic worms. 



