JAWS OF THE ECHINUS. 107 



versify in the different tribes; and, indeed, the 

 number and variety of the parts of which it consists 

 is so great, as hardly to admit of being compre- 

 hended in any general description. In most insects, 

 also, their minuteness is an additional obstacle to 

 the accurate observation of their anatomy, and of 

 the mechanism of their action. The researches, 

 however, of Savigny* and other modern entomolo- 

 gists have gone far to prove, that amidst the 

 infinite variations observable in the form and ar- 

 rangement of the several parts of these organs, 

 there is still preserved, in the general plan of their 

 construction, a degree of uniformity quite as great 

 as that which has been remarked in the fabric of 

 the vertebrated classes. Not only may we re- 

 cognise in every instance the same elements of 

 structure, but we may also trace regular chains 

 of gradation, connecting forms apparently most 

 remote, and organs destined for widely different 

 uses : so that even when there has been a complete 

 change of purpose, we still perceive the same 

 design followed, the same model copied, and the 

 same uniformity of plan preserved in the con- 

 struction of the organs of every kind of mastication ; 

 and there prevails in them the same unity of system 

 as is displayed in so marked a manner in the con- 

 formation of the organs of progressive motion. The 

 jaws, which in one tribe of insects are formed for 

 breaking down and grinding the harder kinds of 

 food, are, in another, fitted for tearing asunder 

 the more tough and fibrous textures : they are 



* See his •' Theorie des Organes de la bouche des Animaiix 

 invertebres et articales," which forms the first part of the " Memoires 

 sur les Animaux sans vertebres." Paris, 1816. 



