42 ON THE TENDENCY OF VARIETIES TO DEPART 



greatest facilities for seizing their prey. Neither did 

 the giraffe acquire its long neck by desiring to reach 

 the foliage of the more lofty shrubs, and constantly 

 stretching it neck for the purpose, but because any 

 varieties which occurred among its antitypes with a 

 longer neck than usual at once secured a fresh range 

 of pasture over the same ground as their shorter-necked 

 companions, and on the first scarcity of food were 

 thereby enabled to outlive them. Even the peculiar 

 colours of many animals, more especially of insects, so 

 closely resembling the soil or leaves or bark on which 

 they habitually reside, are explained on the same 

 principle ; for though in the course of ages varieties 

 of many tints may have occurred, yet those races 

 having colours best adapted to concealment from their 

 enemies would inevitably survive the longest. We have 

 also here an acting cause to account for that balance 

 so often observed in nature, a deficiency in one set 

 of organs always being compensated by an increased 

 development of some others powerful wings accom- 

 panying weak feet, or great velocity making up for 

 the absence of defensive weapons ; for it has been 

 shown that all varieties in which an unbalanced 

 deficiency occurred could not long continue their 

 existence. The action of this principle is exactly 

 like that of the centrifugal governor of the steam 

 engine, which checks and corrects any irregularities 

 almost before they become evident; and in like 

 manner no unbalanced deficiency in the animal king- 

 dom can ever reach any conspicuous magnitude, 



