ORIGIN OF VARIATIONS. 165 



constant, would not be peculiarly specialised as 

 a result. The forces acting upon such an animal 

 are widely different from the forces acting upon 

 an animal which eats the grass at its feet like 

 an ox, or one which must run and climb like a goat 

 or a deer, and the resultant modifications of growth 

 in the several cases must also be different. The 

 principle of increased growth in the direction of 

 the shock resulting from superabundant repair 

 of the momentary compression, explains how the 

 giraffe acquired the phenomenal length of the 

 bones of its fore legs and neck ; and the absence 

 of the shock in the hind quarters shows why they 

 remained undeveloped and absurdly disproportionate 

 to the rest of the body. We may thus recognise 

 in this principle not only the cause of the peculiar 

 difference between the giraffe and other animals, 

 but even of the difference in size between its fore 

 and hind quarters. 



The disturbance which permanently changes 

 the complex combination of forces acting upon a 

 living organ, as has been pointed out, must change 

 the mobile equilibrium existing in the organic 

 processes of growth, waste, and repair. A change 

 in one set of organs entails a change in their rela- 

 tions to adjacent organs, and the forces acting 

 on the latter are accordingly modified. Thus the 



