A HISTORY OF SCIENCE 



their generic and specific characters are determinable, 

 as these are mostly drawn from their solid parts. In 

 quadrupeds, on the contrary, even when their entire 

 skeletons are found, there is great difficulty in discov- 

 ering their distinguishing characters, as these are chiefly 

 founded upon their hairs and colors and other marks 

 which have disappeared previous to their incrustation. 

 It is also very rare to find any fossil skeletons of quad- 

 rupeds in any degree approaching to a complete state, 

 as the strata for the most part only contain separate 

 bones, scattered confusedly and almost always broken 

 and reduced to fragments, which are the only means 

 left to naturalists for ascertaining the species or genera 

 to which they have belonged. 



" Fortunately comparative anatomy, when thorough- 

 ly understood, enables us to surmount all these diffi- 

 culties, as a careful application of its principles in- 

 structs us in the correspondences and dissimilarities 

 of the forms of organized bodies of different kinds, by 

 which each may be rigorously ascertained from almost 

 every fragment of its various parts and organs. 



" Every organized individual forms an entire system 

 of its own, all the parts of which naturally correspond, 

 and concur to produce a certain definite purpose, by 

 reciprocal reaction, or by combining towards the same 

 end. Hence none of these separate parts can change 

 their forms without a corresponding change in the 

 other parts of the same animal, and consequently each 

 of these parts, taken separately, indicates all the 

 other parts to which it has belonged. Thus, as I have 

 elsewhere shown, if the viscera of an animal are so 

 organized as only to be fitted for the digestion of re- 



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