1883.] Growth and Development. 719 
running in the direction and inducing the motion best adapted to 
the good of the organism, will be eventually selected, and the 
others crowded out. If, then, the early local response to touch 
and outgrowth of li mbs or tentacles is followed by an evolution 
of nerves and muscles, out of the many possible directions of 
these nerves and positions of these muscles, those which are of 
advantage to the animal must be selected or the animal will 
perish. 
In the higher animals, then, there is not, as in the lower, a spe- 
cial development of the parts directly exposed to contact. This 
method of development has been succeeded by a development of 
special: channels of force inflow, and of muscles to which motion 
is principally confined. An impression received on one part of 
the body induces growth in another part, in which the affected 
muscle is situated. Yet it must not be supposed that all develop- 
ment of the touched surface at once ceases. It is not enough for 
the nerve to end upon the surface. It must have a peculiar ter- 
mination, specially fitted to receive the contact influence of the 
external force. These contacts are of several distinct kinds, and 
each of them may be readily received by one form of nerve ter- 
mination, but with difficulty by other forms. There is, therefore, 
a natural selection of nerve terminations, the animal best fitted in 
this respect having the advantage. Hence local growth of the 
parts of the surface exposed to touch is succeeded by local modi- 
fication of those parts, to render them delicately sensitive to 
some special mode of touch. Development in response to force 
contact is at first local protusion of motor organs, then a gradual 
evolution of sense organs, nerve fibers and muscles, a convey- 
ance of the contact energy inward from the point of its reception 
to some internal point, and a localization of motor activity and 
growth in internal regions of the body. 
In the very lowest animals we find nothing to indicate the 
existence of even the rudiment of a mind. There is no retention 
p energy. Every excitation powerful enough to make itself felt 
1S responded to by a reflex motion. We cannot fairly credit the 
Ameeba with desire for food and definite motions towards food. 
More probably it moves only in response to external pressure, its 
Movements becoming definite in direction only when this pres- 
Sure is similarly definite. If this be the case then the taking of 
food is a chance result of motions without a fixed purpose. The 
