EPIDERMIC PROTECTION. OTHER ORGANS OF 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 mbrissce 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 



