94 MENTAL EVOLUTION IN ANIMALS. 



having any delicate perception of pitch. I have, however, 

 heard a terrier, which used to accompany a song by howling, 

 follow the prolonged notes of the human voice with some 

 approximation to unison ; and Dr. Huggins, who has a good 

 ear, tells me that his large mastiff " Kepler " used to do the 

 same to prolonged notes sounded from an organ. 



The sense of taste is much more highly developed in the 

 Mammalia than in any other class, and the same general 

 statement applies to the sense of touch. Looking to the 

 class as a whole, the principal organs of the latter are the 

 snout, lips, and tongue ; the modified hairs, or " whiskers," 

 are also very generally present. Among the Rodents, some of 

 the Mustelid?e and all the Primates, the principal organs of 

 touch are the hands. And it would appear that the extreme 

 modification which these members have undergone in the 

 Cheiroptera has been attended with an extraordinary exalta- 

 tion of their power of tactile sensation. For in the celebrated 

 experiment of Spallanzani (since repeated and confirmed by 

 several other observers), it was found that when a Bat is 

 deprived of its eyes, and has its ears stopped up with cotton- 

 wool, it is still able to fly about without apparent inconveni- 

 ence, seeing that it avoids all obstacles in its flight, even 

 though these be but slender strings stretched through the 

 room in which the animal is allowed to fly. The only expla- 

 nation of this surprising fact is that the membranous 

 expanse of the wing, which is richly supplied with nerves, 

 has developed a sensibility to touch, to temperature, or to 

 both, so extreme as to inform the bat of the proximity of a 

 solid body even before contact — either through the increase 

 in the air-pressure as the wing rapidly approaches the solid 

 body, or through the difference in the exchange of heat 

 between the wing and the solid as compared with such ex- 

 change between the wing and the air. When groping our way 

 through a dark room we are ourselves able to feel a large 

 solid body (such as a wall) before we actually touch it, 

 especially, I have observed, with the skin of the face. Pro- 

 bably, therefore, it is a great exaltation of this power which 

 enables these night-flying animals to avoid so slender a solid 

 body as a stretched string. But when we remember the 

 rapidity and accuracy with which the sensation must here be 

 aroused, we may well consider it to equal, if not to surpass, 

 in the domain of touch, the evolutionary development of 



