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, 
