126 ZOOLOGICAL PHILOSOPHY 



3. That their digits, which are never used in making independent 

 movements, will have entirely lost their mobility, become muted 

 and have preserved only the faculty of flexion or extension all 

 together ; 



4. That their thighs, which are continually clasping either the trunk 

 or large branches of trees, will have contracted a habit of always being 

 separated, so as to lead to an enlargement of the pelvis and a back- 

 ward direction of the cotyloid cavities ; 



5. Lastly, that a great many of their bones will be welded together, 

 and that parts of their skeleton will consequently have assumed an 

 arrangement and form adapted to the habits of these animals, and 

 different from those which they would require for other habits. 



This is a fact that can never be disputed ; since nature shows 

 us in innumerable other instances the power of environment over 

 habit and that of habit over the shape, arrangement and proportions 

 of the parts of animals. 



Since there is no necessity to cite any further examples, we may 

 now turn to the main point elaborated in this discussion. 



It is a fact that all animals have special habits corresponding to 

 their genus and species, and always possess an organisation that is 

 completely in harmony with those habits. 



It seems from the study of this fact that we may adopt one or other 

 of the two following conclusions, and that neither of them can be 

 verified. 



Conclusion adopted hitherto : Nature (or her Author) in creating 

 animals, foresaw all the possible kinds of environment in which they 

 would have to live, and endowed each species with a fixed organisa- 

 tion and with a definite and invariable shape, which compel each 

 species to five in the places and climates where we actually find them, 

 and there to maintain the habits which we know in them. 



My individual conclusion : Nature has produced all the species 

 of animals in succession, beginning with the most imperfect or simplest, 

 and ending her work with the most perfect, so as to create a gradually 

 increasing complexity in their organisation ; these animals have 

 spread at large throughout all the habitable regions of the globe, 

 and every species has derived from its environment the habits that 

 we find in it and the structural modifications which observation 

 shows us. 



The former of these two conclusions is that which has been drawn 

 hitherto, at least by nearly everyone : it attributes to every animal 

 a fixed organisation and structure which never have varied and never 

 do vary ; it assumes, moreover, that none of the locaUties inhabited 

 by animals ever vary ; for if they were to vary, the same animals 



