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ANIMAL MECHANISM. 



These very facts are, however, interpreted in an opposite 

 sense by the partisans of the invariability of species ; they 

 seem to find an unanswerable argument in support of their 

 cause, in the return to the primitive type, when the modifying 

 influences have ceased. 



To w^hat conclusion can we come when we meet with these 

 contrary opinions ? It must be that the partisans of develop- 

 ment have not completed their task, and that they ought to 

 add new proofs to those which they have already given. It 

 is to experiment that the principal part belongs, while theory 

 is not without its importance ; by causing us to foresee in what 

 manner a certain kind of function ought to modify a muscle, 

 it will give its proper value to the modification which may 

 subsequently be obtained. Indeed, without theory, the ex- 

 perimenter can seldom recognize the modification which he 

 has observed. We seldom find in anatomy anything but 

 that which we seek for, especially when we have to do with 

 slight variations like those which we might hope to produce 

 in the organism of an animal. 



The experiments to be tried are tedious and troublesome ; 

 their plan, however, is easy to trace. 



If man, adapting to his necessities the domestic animals, 

 has already succeeded in modifying their organization within 

 certain limits, he has produced these changes, as we may 

 say, fortuitously. Only intending, for example, to obtain 

 draught horses or racers, it was not necessary to place 

 the species under conditions entirely artificial. This must, 

 however, be done, if we aim at elucidating the problem of 

 which we speak, and of carrying to the farthest possible 

 limit, changes in the conditions of the mechanical work of 

 animals. 



Man has utilized the aptitudes of difterent animals, rather 

 than sought to give them new ones. It would be necessary 

 to do violence to the habits of animals, and to constrain 

 them gradually to perform acts to which their organism is 

 but slightly adapted. If, in order to get its food, a species 

 with an organization unsuitable for leaping, should be com- 

 pelled to take leaps of gradually greater height, everything 

 leads us to suppose that it would acquire at length great 



