OF ANIMALS. 



169 



double, and, consequently, the nostrils quadruple, a pair for each snout. This 

 powerful inlet of pleasure to fishes often proves fatal to them from its very 

 perfection ; for several kinds are so strongly allured by the odour of majorum, 

 asafcEtida, and other aromas, that by smearing the hand over with these sub- 

 stances, and immersing it in the water, they will often flock towards the fin- 

 gers, and in their intoxication of delight may easily be laid hold of. And 

 hence the angler frequently overspreads his baits with the same substances, 

 and thus arms himself with a double decoy. 



There can be no doubt of the existence of the same sense in insects ; for 

 they possess a very obvious power of distinguishing the odorous properties 

 of bodies, even at a considerable distance beyond the ran^e of their vision ; 

 but the organ in which this sense resides has not been satisfactorily pointed 

 out : Reimar supposes it to exist in their stigmata, and Knoch in their ante 

 rior pair of feelers. 



The general organ of hearing is the ear, but not always so ; for in most 

 of those who hear by the Eustachian tube only, it is the mouth, and in the 

 whale tribes the nostrils or blow-hole. It is so, however, in all the more 

 perfect animals, which usually for this purpose possess two distinct entrances 

 into the organ ; a larger and external, surrounded by a lobe ; and a smaller 

 and internal, opening into the mouth. It is this last which is denominated 

 the Eustachian tube. The shape of the lobe is seldom found even in mam- 

 mals similar to that in man, excepting among the monkey and the porcupine 

 tribes. In many kinds there is neither external lobe nor external passage. 

 Thus, in the frog, and most amphibious animals, the only entrance is the 

 internal, or that from the mouth ; and in the cetaceous tribes the only effective 

 entrance is probably of the same kind; for, though these may be said to pos- 

 sess an external aperture, it is almost imperceptibly minute. It is a curious 

 fact, that, among the serpents, the blind-worm or common harmless snake is 

 the only species that appears to possess an aperture of either sort ; the rest 

 have a rudiment of the organ within, but we are not acquainted with its being 

 pervious to sound. 



Fishes are well known to possess a hearing organ, and the skate and shark 

 have the rudiment of an external ear ; but, like other fishes, they seem chiefly 

 to receive sound by the internal tubule alone. 



That insects in general hear is unquestionable, but it is highly questionable 

 by what organ they obtain the sense of hearing. The antennas, and perhaps 

 merely because we do not know their exact use, have been supposed by many 

 naturahsts to furnish the means ; it appears fatal, however, to this opinion to 

 observe, that spiders hear, though they have no true antennas, and that other 

 insects which possess them naturally seem to hear as correctly after they are 

 cut off. 



The sense of vision exhibits perhaps more variety in the different classes 

 of animals than any of the external senses. In man, and the greater number 

 of quadrupeds, it is guarded by an upper and lower eyelid ; both of which 

 in man, but neither of which in most quadrupeds, are terminated by the addi- 

 tional defence and ornament of cilia or eyelashes. In the elephant, opossum, 

 seal, cat-kind, and various other mammals, all birds, and all fishes, we 

 find a third eyelid, or nictitating membrane, as it is usually called, arising 

 from the internal angle of the eye, and capable of covering the pupil with a 

 thin transparent veil, either wholly or in part, and hence of defending the eyes 

 from danger in their search after food. In the dog this membrane is narrow ; 

 in oxen and horses it will extend over half the eyeball ; in birds it will easily 

 cover the whole ; and it is by means of this veil, according to Cuvier, that the 

 eagle is capable of looking directly against the noonday sun. In fishes it is 

 almost always upon the stretch, as in their uncertain element they are ex- 

 posed to more dangers than any other animal. Serpents have neither this 

 nor any other eyelid ; nor any kind of external defence whatever but the 

 common integument of the skin. 



The largest eyes in proportion to the size of the animal belong to the bird 

 tribes, and nearly the smallest to the whale; the smallest altogether to 



