220 



ICHTHYOLOGY. 



Introduc- cautiously they avoid his lure, and with what discrimination 



tion, j^igy sometimes prefer one colour or kind of artificial fly to 



The Senses, another, must be impressed with the belief that the vision, 



^■^^/"^ at least of certain species, is by no means devoid of clearness 



and precision. 



Fig. 47. 

 Shows the large eyes of Sebasies percoideSt one of the Scleropenidw or Trigll- 

 dcc, a family whose home is at the bottom of the sea. and have very com- 

 monly the lower rays of the pectoral fins detached and organized as feelers. 



We shall not repeat here the notices that we have already 

 had occasion to take of the organ of hearing. In Sharks, a 

 canal extends from the interior organ of hearing to the 

 hinder part of the head, where it is closed by the skin, and 

 in the rays there is a very minute external orifice to the 

 canal, closely approximated on the dorsal aspect of the 

 head to its fellow. In osseous fishes there is no such me- 

 chanism, and the sonorous vibrations are conveyed to the 

 labyrinth through the solid parts ; but in the Carp and 

 certain Siluroids, the air-bladder would appear to be ac- 

 cessory to the acoustic organ, as it is connected with it by 

 a chain of ossicles. The general structure of the organ 

 of hearing in fishes is doubtless specially adapted for the 

 sensation of the sonorous undulations of the element in 

 which they live. 



A few lines may now be devoted to the consideration of 

 the sense of smell. The nostrils of fishes are not so placed 

 as to be traversed by 

 the respiratory me- 

 dium in its course to 

 the organs of respi- 

 ration. They con- 

 sist merely of two 

 openings, situate on 

 the muzzle, and 

 lined by the pitu- 

 itary membrane, 

 which is raised in 

 extremely regular 

 folds. Their shape is 

 sometimes oblong, 

 sometimes round or 

 oval. They are 



placed either at the "^ 



end of the muzzle Fig. 48. 



or on its sides ; some- 

 times on its su- 

 perior face, and even occasionally, as in Skates (fig. 48), 

 and Sharks, on its under surface near the angle of the mouth. 

 In the Lamprey they are approximate on the top of the head, 

 and open by one common orifice (fig. 49). In the great ma- 



distance. These are what are called double nostrils, an Introdrc- 

 inaccurate term, in as far as each pair of holes leads only tion. 

 to a single cavity. The margins of the anterior orifice are ''''" Senses, 

 often tubular, as in the Eel, and sometimes a single side ^^"V^^ 

 of the tubular margin is prolonged into a tentacular 

 appendage, as in several Siluri. In the genus Lophius the 

 nostrils are borne upon a little pedicle, so as somewhat to 

 resemble mushrooms. Various other modifications are 

 observable in different genera, although not necessary to be 

 here narrated. 



It is certain that fishes possess the faculty of perceiving 

 odours ; that various scents attract or repel them ; and 

 there is no reason to doubt that the seat of that perception 

 lies in the nostrils. It may be reasonably conjectured, that 

 its strength depends mainly on the degree of development 

 produced by the number and extent of the interior folds 

 of the pituitary membrane. 



The essential character of the organ of smell in fishes is 

 that the pituitary sac has one or more external openings not 

 commimicating with the mouth or fauces except in the 

 Dermopteri, and in these the naso-palatine canal is not 

 traversed by the water in its course to the gills. In some 

 Synbranchidte, the posterior nasal aperture is situate on the 

 white parts, within the edge of the lip, in this respect agree- 

 ing with the Lepidosiren. Long debates on the conflicting 

 claims of the latter to be ranked as a fish or a reptile, have 

 turned on the position of the posterior nostril. Telrodon 

 naritiis is an exception to the general rule of double nos- 

 trils, in having merely a single wide opening, coextensive 

 with the dimensions of the pituitary sac, but bordered by 

 membrane. In other Tetrodons the sac is closed by a thin 

 membrane, in which there are two small openings close to 

 each other. The Chromidce also, and the Ctenoid Lahridce, 

 have but one opening to each sac ; and in some few. fishes 

 there is a barbel merely, without an aperture, in place of a 

 nostril. 



In regard to the sense of taste in fishes, it is evident that 

 as, with few exceptions, they swallow their food rapidly and 



Nostrils of Raia Lemprieri, an Australian 

 Skate. 



Fig. 49. 



Head of Petromyzon mordax. showing the single nostril tnbo and scrcn 



branchial orifices. 



jority of fishes each nostril opens by two orifices, the one 

 posterior to the other, and in some cases at a considerable 



Fig. 50. 

 Month of Flotositx mfgastomus. one of the Silnrida:. This fish feeds at the 

 bottom, and the barbels developed round the mouth are organs of touch. 

 Teeth are seated on the inner lips and move with them. 



without mastication, their perception of that faculty must 

 be in noways acute. The same may be inferred from the 

 fact of their tongue being almost immoveable, often entirely 

 osseous, or beset with teeth or dental plates, and from its 

 receiving very slender nerves, and these but few in number. 

 Even those species of which the jaws are so armed as to 

 enable them to cut and bruise their aliment, cannot long 

 retain the latter in their mouths, on account of the position 

 and the play of the respiratory organs. No salivary glands 

 discharge their moisture on the organs of taste. The tongue 

 itself is not seldom entirely wanting ; and even when it 



