EPIDERMIC PROTECTION.—OTHER ORGANS OP TOUCH. 391 
communicating with each other at great distances. It has 
often been observed, for instance, that, when a straggler is 
attacked, at the distance of several miles from a “ school,” a 
number of its fellows bear down to its assistance in an almost 
incredibly short space of time. It can scarcely be doubted 
that the communication is made through the medium of the 
vibrations of water, excited by the struggles of the animal, or 
perhaps by some peculiar movements specially adapted for 
this purpose, and propagated through the liquid to the 
immense surface of the skin of the distant Whales. 
492. The sensibility of the true skin would be too great, if 
it were not protected by the Epidermis (§ 38), the thickness 
of which varies considerably, according as the part is to be 
endowed with acute sensibility, or to be protected from impres¬ 
sions of too strong a nature. Thus it is particularly thin at the 
ends of the fingers, and on the surface of the lips, which are 
used for feeling; but is thick on the palm of the hand, which 
is used for firmly grasping , and which would be continually 
suffering pain if its sensibility were too acute; and it is still 
thicker on the sole of the foot, especially on the heel and the 
ball of the great toe, where pressure has to be sustained. 
493. Although the fingers of Man and of the Quadrumana, 
being endowed with peculiar sensibility, are their special organs 
of touch , yet we find that they cease to be so in most of the 
other Mammalia, whose extremities are adapted only for sup¬ 
port and locomotion, and are terminated by hard claws or 
hoofs that completely envelop them. In many of these, we 
find the lips and tongue employed as the chief organs of touch ; 
in the Elephant, this sense is evidently possessed very acutely 
by the little finger-like projection at the end of its trunk; and 
in several other cases the vibrissce or whiskers are its special 
instruments, the bulbs of their long stiff hairs being copiously 
supplied with sensory nerves. 
494. A curious modification of the sense of Touch appears 
to exist in Bats. It has been found that these animals, when 
deprived of sight and (as far as possible) of hearing and smelling 
also, still flew about with equal certainty and safety, avoiding 
every obstacle, passing through passages only just large enough 
to admit them, and flying through places with which they 
were previously unacquainted, without striking against the 
objects near which they passed. The same result happened 
