GEOFFROY AND CUVIER 75 



1 



clearest way the radical opposition between the functional 

 and the formal attitudes to living things. 



Cuvier points out that if by unity of composition is meant 

 identity, then the statement that all animals show the same 

 composition is simply not true compare a polyp with 

 a man ! on the other hand, if by unity is meant simply 

 resemblance or homology, the statement is true within certain 

 limits, but it has been employed as a principle since the days 

 of Aristotle, and the theory of unity of composition is original 

 only in so far as it is false. He admits, however, that 

 Geoffrey has seized upon many hidden homologies, especially 

 by his valuable discovery of the importance of foetal structure. 

 In all this Cuvier is undoubtedly right. Unity of plan and 

 composition, as Geoffrey conceived it, simply does not exist. 

 Cuvier goes on to say that this principle of Geoffrey's, in 

 the greatly modified form in which it can be accepted, and 

 has been accepted from the dawn of zoology, is not the sole 

 and unique principle of the science. On the contrary, it is 

 merely a subordinate principle, subordinate to a higher and 

 more fruitful principle, that, namely, of the conditions of 

 existence, of the adaptation (convenance) of the parts, of 

 the co-ordination of the parts for the role which the animal 

 is to play in Nature. " That is the true philosophical 

 principle," he says, " whence may be- deduced the possibility 

 of certain resemblances, the impossibility of certain others ; 

 it is the rational principle from which follows the 

 principle of the unity of plan and composition, and in 

 which at the same time it finds those limits, which some 

 would like to disregard " (p. 248). 



Geoffrey's position is the direct contrary. He holds that 

 the principle of the unity of plan and composition is the 

 true base of natural history, 1 and that this unity limits the 

 possible transformations of the organism. Thus, speaking of 

 the influence of the respiratory medium, he says, " All the same 

 this influence of the external world, if it has ever become 

 a cause which disturbed organisation, must necessarily have 

 been confined within fairly narrow limits ; animals must have 

 opposed to it certain conditions inherent to their nature, 

 the existence of the same materials composing them, and a 



1 MammifcreS) i., Discours prel., p. 18. 



