718 Growth and Development. |July, 
tact of heat. The tongue receives the finer contacts of liquid, 
and the nasal nerves of gaseous matter. The coarser range of 
vibratory influences acts upon the nerves through the medium of 
the ears, and the finer range through the eyes. Thus the body is 
like a highly delicate instrument, upon which nature plays witha 
thousand fingers, and which responds to the faintest touch of 
physical force, though it cannot act of itself any more than the 
piano can yield music without a pressure upon its keys. 
But an important secondary result flows from this primary rela- 
tion of organisms to outer nature. Contact induces oxidation. 
Nutrition follows. Growth takes place in the active regions of 
the body, but not in the passive. In the study of the genesis of a 
the species particular attention must be given to this fact. The 
parts of the body which come most into contact with external 
substances, and move most readily in response thereto, are those — 
which grow and vary most rapidly. This is particularly the c 
in the lowest animals, in which a developed nervous organization 
is yet wanting. In them contact induces motion in the corm 
ous surfaces. Local growth follows. Protrusion of sensitive and 
active tentacles results. 
In the higher animals, in which a nervous system has been de- 
veloped, a different result of external contact appears. The pe 
tion induced takes place at some internal point, and it 1$ heb: i 
the subsequent growth occurs. Thus the influences which ie 
local growth in low forms mry be generally distributed pris 
out higher forms, and the great power which external ener 
to mold the surface regions of the one, is reduced to a mini 
in the case of the other. We may look upon ext ker ale 
first inducing a genesis of pseudopodia, tentacles and other 1 
appendages ; and as next inducing a genesis of war iak 
nerve organs and muscles. A surface exposed to repeat ye 
both grows more sensitive to touch, and the sett E 
gradually makes its way inward, though protap r o 
Every habitual touch either signifies some peril, oF ghest good io 
condition to which the organism must res ied 
is to be attained. The more readily it respon 
its motions, and the more adapted they are ast ye 
* . ` . 4 u h 
animal, the more likely is it to survive. Thus, mre 
channels leading inward from a sensitive surface Mis yet 
f motions, o 
direction, and induce a great variety O 
