OF TASTE. 81 



Fishes are probably still less favored in this respect. As they 

 perceive odours through the medium of water, we should anti- 

 cipate that the structure of their apparatus would be different 

 from that of animals which breathe air. Their nostrils are 

 mere superficial pouches, lined with a membrane gathered into 

 folds, which generally radiate from a centre, but are sometimes 

 arranged in parallel ridges on each side of a central band. As 

 the perfection of smell depends on the amount of surface ex- 

 posed, it follows that those fishes which have these folds most 

 multiplied are also those in which this sense is most acute. 



168. No special apparatus for smell has yet been found 

 in the invertebrata. And yet there can be no doubt that insects, 

 crabs, and some mollusca perceive odours, since they are at- 

 tracted from a long distance by the odour of objects. Some of 

 these animals may be deceived by odours similar to, those of 

 their prey ; which clearly shows that they are led to it by this 

 sense. The carrion fly will deposit its eggs on plants which 

 have the smell of tainted flesh. 



4. Or TASTE. 



169. TASTE is the sense by which the flavour of bodies is 

 perceived. That the flavour of a body may be perceived, it 

 must come into immediate contact with the nerves of taste, 

 and hence these nerves are distributed at the entrance to 

 the digestive tube, on the surface of the tongua and the palate. 

 By this sense animals are guided in the choice of their food, 

 and warned to abstain from what is noxious. There is an 

 intimate connexion between taste and smell, so that both 

 these senses are called into requisition in the selection of 

 food. 



1/0. The nerves of taste are not so strictly special as those 

 of sight and hearing. They do not proceed from one single 

 trunk ; and, in the embryo, do not correspond to a particular 

 part of the brain. The tongue receives nerves from several 

 trunks ; and taste is perfect in proportion as the nerves which 

 go to the tongue are more minutely distributed. The extremi- 

 ties of the nerves generally terminate in the little asperities of 

 the surface, called papillce. Sometimes these papillae are very 

 harsh, as in the cat and the ox ; and, again, they are very deli- 

 cate, as in the human tongue, in that of the dog, horse, &c. 



171. Birds have the tongue cartilaginous, sometimes be- 



o 



