CHAP. XIII.] LOWER ANIMALS. 207 



such as ducks, snipes, and woodcocks which push their long bills 

 into the mud, the point of the mandible is not only comparatively 

 soft, but is often covered with a very thin membranous skin, 

 which evidently implies considerable sensibility." 



In the majority of Quadrupeds this sense is perhaps 

 not very highly developed, though as in birds it seems 

 to be principally localized in the paws and lips. There 

 are, however, two remarkable exceptions. The trunk of 

 the Elephant is evidently endowed with a very keen and 

 discriminative sense of touch, and is to some extent put 

 to the same kind of use as the four hands of Quadrumana, 

 or the two of human beings. The tactile endowments of 

 all these parts, however, in regard to mere sensitiveness, 

 are altogether thrown into the shade by the second excep- 

 tion above referred to viz., that presented by the inter- 

 digital membranes, or so-called wings of Bats, and by the 

 skin over their large ears. The sensitiveness of these 

 parts is so marvellous that it can take the place of sight, 

 and enables Bats to avoid even the most delicate obstacles 

 in their tortuous and rapid flight. As Spallanzani first 

 observed, these animals will, even when they have been 

 blinded, " guide themselves through the most winding and 

 complicated passages without once hitting the walls, or 

 striking against any impediment which may seem to 

 obstruct their progress." When in this condition they 

 can even avoid coming into collision, during their rapid 

 gyrations, with threads of silk which have been purposely 

 stretched across a gallery or passage. 



The three senses already referred to constitute the 

 special intellectual senses of man those upon which 

 most of his knowledge of the external world is based. 

 There is, however, another sensorial endowment the 

 sense of Smell which, though it pla^ s a very inconsider- 



