THE DOCTEINE OF FINAL CAUSES. 4:83 



into a prominent position by the struggle of two antagonistic schools of 

 physiologists. On the one hand, it has been maintained that thia 

 doctrine of final causes is altogether unphilosophical, and requires tc 

 be replaced by a more comprehensive and profound principle : on the 

 other hand, it is* asserted that the doctrine is not only true, but that, 

 in our own time, it has been fixed and developed so as to become the 

 instrument of some of the most important discoveries which have been 

 made. Of the views of these two schools we must endeavor to give 

 some account. 



The disciples of the former of the two schools express their tenets 

 by the phrases unity of plan, unity of composition ; and the more 

 detailed developement of these doctrines has been termed the Theory 

 of Analogies, by Geoffrey Saint-Hilaire, who claims this theory as his 

 own creation. According to this theory, the structure and functions 

 of animals are to be studied by the guidance of their analogy only ; 

 our attention is to be turned, not to the fitness of the organization for 

 any end of life or action, but to its resemblance to other organizations 

 by which it is gradually derived from the original type. 



According to the rival view of this subject, we must not assume, 

 and cannot establish, that the plan of all animals is the same, or their 

 composition similar. The existence of a single and universal system 

 of analogies in the construction of all animals is entirely unproved, 

 and therefore cannot be made our guide in the study of their pro- 

 perties. On the other hand, the plan of the animal, the purpose of its 

 organization in the support of its life, the necessity of the functions to 

 its existence, are truths which are irresistibly apparent, and which 

 may therefore be safely taken as the bases of our reasonings. This 

 view has been put forward as the doctrine of the conditions of 

 existence : it may also be described as the principle of a purpose ir : 

 organization ; the structure being considered as having the function 

 for its end. We must say a few words on each of these views. 



It had been pointed out by Cuvier, as we have seen in the last 

 chapter, that the animal kingdom may be divided into four great 

 branches; in each of which the plan of the animal is different, 

 namely, vertebrata, articulata, mollusca, radiata. Now the question 

 naturally occurs, is there really no resemblance of construction in 

 these different classes ? It was maintained by some, that there is such 

 a resemblance. In 1820, 1 M. Audouin, a young naturalist of Paris, 



1 CUT. Hist. Sc. Nat. iii. 42 



