ADAPTATION 119

Adaptation.—Wherever we look in the world of
organisms we find examples of adaptation; we see
form suited for different kinds of motion, organs
suited for their uses, constitution suited to circum-
stances in such external features as colouring and
in such internal adjustments as the regulation of
temperature; we find effective weapons and effective
armour, flowers adapted to insect visitors and insect
visitors adapted to flowers, one sex adapted in
relation to the other, the mother adapted to bearing
and rearing offspring, the embryo adapted to its pre-
natal life; everywhere there is adaptation in varying
degrees of perfection. The adaptation is a fact, in
regard to which all naturalists are agreed; difference
of opinion arises when we ask how these adaptations
have come to be.

In the chapter " Adaptation" Spencer practically
restricted his attention to a certain kind of adapta-
tion, namely the direct modifications which result
from use or disuse, or from environmental influence.
The blacksmith's arm, the dancer's legs, the jockey's
crural adductors, illustrate direct results of practice;
" a force de forger on devient forgeron." The skin
forms protective callosities where it is much pressed
or rubbed, as on the schoolboy's hands or the old
man's toothless gums. The blood-vessels may re-
spond by enlargement to increased demands made
on themj the fingers of the blind become extra-
ordinarily sensitive.

Spencer points to the general truth that extra
function is followed by extra growth, but that a
limit is soon reached beyond which very little, if any,
further modification can be produced. Moreover, extent of the damage