Adaptation - 63 
contrary instinct. This moth does not fly away from danger, but 
“feigns death,” that is, it draws antennae, legs and wings close to the 
body, and remains perfectly motionless. It may be touched, picked 
up, and thrown down again, and still it does not move. This remark- 
able instinct must surely have developed simultaneously with the 
wood-colouring; at all events, both cooperating variations are now 
present, and prove that both the external and the most minute 
internal structure have undergone a process of adaptation. 
The case is the same with all structural variations of animal 
parts, which are not absolutely insignificant. When the insects 
acquired wings they must also have acquired the mechanism with 
which to move them—the musculature, and the nervous apparatus 
necessary for its automatic regulation. All instincts depend upon 
compound reflex mechanisms and are just as indispensable as the 
parts they have to set in motion, and all may have arisen through 
processes of selection if the reasons which I have elsewhere given for 
this view are correct}. 
Thus there is no lack of adaptations within the organism, and 
particularly in its most important and complicated parts,so that we may 
say that there is no actively functional organ that has not undergone 
a process of adaptation relative to its function and the requirements 
of the organism. Not only is every gland structurally adapted, down 
to the very minutest histological details, to its function, but the 
function is equally minutely adapted to the needs of the body. 
Every cell in the mucous lining of the intestine is exactly regulated 
in its relation to the different nutritive substances, and behaves in 
quite a different way towards the fats, and towards nitrogenous 
substances, or peptones. 
I have elsewhere called attention to the many adaptations of the 
whale to the surrounding medium, and have pointed out—what has 
long been known, but is not universally admitted, even now—that in 
it a great number of important organs have been transformed in 
adaptation to the peculiar conditions of aquatic life, although the 
ancestors of the whale must have lived, like other hair-covered 
mammals, on land. I cited a number of these transformations—the 
fish-like form of the body, the hairlessness of the skin, the trans- 
formation of the fore-limbs to fins, the disappearance of the hind- 
limbs and the development of a tail fin, the layer of blubber under 
the skin, which affords the protection from cold necessary to a warm- 
blooded animal, the disappearance of the ear-muscles and the auditory 
passages, the displacement of the external nares to the forehead for 
the greater security of the breathing-hole during the brief appearance 
at the surface, and certain remarkable changes in the respiratory and 
circulatory organs which enable the animal to remain for a long time 
1 The Evolution Theory, London, 1904, p. 144. 
