120 



THE VITAL FUNCTIONS. 



atioiis observable in the form and arrangement 

 of the several parts of these organs, there is still 

 preserved, in the general plan of their con- 

 struction, a degree of uniformity quite as great 

 as that which has been remarked in the fabric 

 of the vertebrated classes. Not only may we 

 recognise in every instance the same elements 

 of structure, but we may also trace regular 

 chains of gradation, connecting forms appa- 

 rently 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 pre- 

 served in the construction 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 conformation 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 fa- 

 shioned, in a third, into instruments for taking 

 up the semi-fluid honey prepared by flowers; 

 while, again, in a fourth, they are prolonged 

 and folded into a tubular proboscis, capable of 

 suction, and adapted to the drinking of fluid 

 aliment. Pursuing the examination of these 

 organs in another series of articulated animals, 



