ON THE METHOD OF PALEONTOLOGY 433 



one another : there are physiological correlations and there are 

 morphological correlations. Thus the teeth and the stomach are 

 physiologically correlated, contributing as they do to the common 

 end of alimentation ; and inasmuch as this coadaptation towards a 

 common end is the very essence of physiological correlation, the latter 

 has sometimes received the name of rational correlation ; for when 

 the result to which a combination tends is obvious, we commonly 

 imagine we can see the reason for that combination. 



Since the validity of nine-tenths of the science of animal physi- 

 ology involves the admission, that multitudes of the parts of animals 

 are organs working towards a common end, I do not suppose that it 

 ever has entered, or ever will enter, into the mind of any person 

 conversant with the rudiments of that science to question the exist- 

 ence of physiological correlation between the different parts of 

 animals. But how far that correlation is in any case to be called neces- 

 sary ; that is, how far in order to the due performance of a given 

 function in any case it is impossible that the organs performing that 

 function should be different from what we find them to be, is quite 

 another question. Thus the teeth of a lion and the stomach of the 

 animal are in such relation that the one is fitted to digest the food 

 which the others can tear ; they are physiologically correlated, but we 

 have no reason for affirming this to be a necessary physiological 

 correlation, in the sense that no other could equally fit its 

 possessor for living on recent flesh. The number and form of the 

 teeth might have been quite different from that which we know it to 

 be, and the construction of the stomach might have been greatly 

 altered, and yet the function of these organs might have been equally 

 well performed. Nothing can be more uniform than the physiological 

 ends which have to be attained by living beings ; nothing more 

 various than the modes in which they are attained ; and it would, I 

 think, in the face of these well-known facts, be the height of presump- 

 tion to affirm that the function which we see in any case performed 

 in a particular way could not possibly have been performed in any 

 other mode. 



If physiological correlations are however not necessary ; if, so far 

 as physiology is concerned, we have no right to say with Cuvier, that 

 " Every organized being constitutes a whole, a single, and complete 

 system, whose parts mutually correspond and concur by their 

 reciprocal reaction to the same definite end. None of these parts can 

 be changed without affecting the others, and consequently each taken 

 separately indicates and gives all the rest ; " — then a very important 

 consequence follows, viz., that it is quite impossible to reason conclu- 



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