VARTABTLITY OF THE MUSCULAR SYSTEM. 101 



facilities for leaping. If the descendants of these animals 

 retained any of the power of their ancestors, they might per- 

 haps, in their turn, develop still more this faculty of leaping. 

 Graduating thus the effort imposed on this particular species, 

 no longer in a utilitarian point of view, which there would 

 be no inducement to surpass, but requiring indefinitely more 

 force or greater extent in the play of the muscles, we might 

 hope that the anatomical development would increase indefi- 

 nitely, and that we might obtain something analogous to that 

 which is now called the passage of one species into another. 



What we have said of the muscular function applies to all 

 the rest. By modifying in a gradual manner the conditions 

 of the food of animals, as well as those of light and dark- 

 ness, temperature, and atmospheric pressure under which they 

 may be made to live, we may impress upon their organism 

 modifications analogous to those which zoologists have already 

 observed under the influence of climate, and of the various 

 atmospheric conditions and different altitudes in which animals 

 have been placed by nature. These changes, brought about 

 by well-managed transitions always tending to the same end, 

 would have a chance of producing considerable transformations 

 in animal organization, provided that, by persevering determi- 

 nation, these efforts were indefinitely accumulated ; as in the 

 case of breeders of animals, who use similar means for the 

 production of selected kinds of stock. 



We will proceed no farther in the field of hypothesis, but 

 we will, in conclusion, make an appeal to zealous experimen- 

 talists. Many who have been convinced of the great import- 

 ance of this enquiry seem already to be engaged in this 

 enterprise. What question, in fact, can more nearly concern 

 the human race than this : Can our species he modified ? 

 According to the tendency which may be given to it, can it be 

 directed either towards perfection, or degradation ? 



