JAWS OP ARTICULATA. 121 



we find them gradually assuming the characters, 

 as well as the uses of instruments of prehension, 

 of weapons for warfare, of pillars for support, of 

 levers for motion, or of limbs for quick pro- 

 gression. Some of these remarkable metamor- 

 phoses of organs have already attracted our 

 attention in a former part of this treatise.* Jaws 

 pass into feet, and feet into jaws, through every 

 intermediate form ; and the same individual 

 often exhibits several steps of these transitions ; 

 and is sometimes provided also with super- 

 numerary organs of each description. In the 

 Arachnida, in particular, we frequently meet with 

 supernumerary jaws, together with various ap- 

 pendices, which present remarkable analogies of 

 form with the antennae, and the legs and feet of 

 the Crustacea. 



The principal elementary parts which enter 

 into the composition of the mouth of an insect, 

 when in its most perfect state of developement, 

 are the seven following: a pair of upper jaws, 

 a pair of lower jaws, an upper and a lower lip, 

 and a tongue. t These parts in the Locusta 



* Vol. i. p. 289. 



t All these parts, taken together, were termed by Fabricius 

 instruinenta cibaria ; and upon their varieties of structure he 

 founded his celebrated system of entomological classification. 

 Kirby and Spence have denominated them trophi. See their 

 Introduction to Entomology, vol. iii. p. 417. To the seven 

 elements above enumerated Savigny adds, in the Hemiptera, an 

 eighth, which he terms the Epiylossa. 



