pensated for the want of this essential condition 

 of sight, nature has denied them a visual ap- 

 paratus altogether as in the case of the mole, 

 which has no optic nerve, and an eye so small, 

 that its existence has been doubted. 



We come next to the function of hearing. In 

 the very lowest tribes of animals it appears that 

 this function, like those of smell and sight, is 

 merely a more delicate kind of touch, and per- 

 formed equally by the whole surface of the body. 

 The greater number of animals of this descrip- 

 tion have no obvious auditory apparatus, the 

 cuttle being among the few exceptions, and fur- 

 nishing, perhaps, the best example of an ear in its 

 rudimental state. In this animal it consists mere- 

 ly of a membranous bag filled with liquid, si- 

 tuated in a tubercle of the cartilaginous ring 

 which surrounds the gullet, and surrounded on 

 all sides by cartilage. Upon the outer surface of 

 this bag is distributed the auditory nerve ; while, 

 within the liquid which it contains, are some 

 little pieces of earthy matter, presumed to be 

 necessary to render the vibrations of the liquid, 

 on which sound depends, sufficiently forcible to 

 make the requisite impression on the nerve. 



In the greater number of insects, also, the au- 

 ditory apparatus is very obscure ; although it is 

 certain that they do hear, and even very acutely. 

 The immediate seat of the function has been pre- 

 sumed to be the membrane which connects their 

 antennae with the head but spiders hear which 



