ICHTHYOLOGY. 



67 1 



Mroctoie ceive the approach of their foes, and it is the principal 

 md instrument by which they obtain their food. The aina- 

 ***" teur in artificial fly-fishing often tempts the fish with 

 ~^ one kind of fly, but in vain ; and upon substituting ano- 

 ther in its place of a different form or colour, he suc- 

 ceeds in the capture. These motions of the fish are all 

 regulated by the eye ; hence some fish will bite as rea- 

 dily at a bit of red cloth as at a piece of flesh. 



As this organ exercises a very powerful influence on 

 the habits of fishes, it should be carefully attended to 

 by the systematic ichthyologist. The characters which 

 are furnished by its form and position are nut liable to 

 variations, and they are sufficiently obvious. Those 

 furnished by the colours of the different parts hold a se- 

 condary rank. They are not very liable to vary, but 

 they experience great changes after death, and should 

 be used with very great caution. 



S. Organ* of hearing. It was long known to na- 

 turalists, that fishes possessed some means of distinguish- 

 ing the vibrations of sonorous bodies. Trouts and carp 

 have been taught to come to a particular place of the 

 pond for food upon a bell being rung ; and a drum has 

 sometimes been employed to drive fishes into a net. In 

 general, however, it was supposed that the vibrations 

 communicated to the water, became sensible to the fish, 

 through the medium of the organs of touch. 



The Abbe Nollet (in the Hi>t. tie f.lcid. R. det Scien. 

 ut, 1743, p. 26.) ascertained by conclusive experi- 

 ment*, that the human ear was susceptible to the im- 

 pression* of sound, even when immersed in water. This 

 di*corery excited the attention of anatomist* to the 

 structure of the organ* of hearing, and Camper, Geof- 

 rrot, and Vicq d'Axyr, succeeded in pointing out the 

 nature of the different parts. Our illustrious country- 

 man Dr Monro, in his work on the structure and phy- 

 siology of fishes, contributed to enlarge our knowledge 

 of the organs of hearing by numerous accurate dissec- 

 tions. 



In the osseous fishes, no external ear has hitherto 

 been detected, and the same remark is applicable to 

 those cartilaginous fishes which have free brant-hie. But 

 in the cartilaginous fishes with fixed branching small 

 apertures have been discovered leading to auditory or- 

 gan*. These were first observed by Monro in the skate 

 and the angel shark. In the former fi-li they occur in 

 the back part of the occiput, near the joining of the 

 head with the spine. They are two in number, not lar- 



Cthan to admit the head of a small pin ; and in a large 

 are found at the distance of an inch from each other. 

 In ftsbe* that have free branchiae, the internal organs 

 of hearing are situated in the sides of the cavity of the 

 cranium, and fixed there by a cellular tissue, consisting 

 of vessels, and osseous or cartilaginous fracna. In the 

 fishes with fixed brauchia-, those organs are inclosed in 

 a particular cavity formed in the substance of the cra- 

 nium. Thi* cavity is situated on the side and posterior 

 Kof that which contain* the brain, with which it 

 not communicate, except by the hole* that afford 

 passage* for the nerve*. The sac exhibit* many differ, 

 ences as to size and form in the different species. Be- 

 side* the ordinary viscid fluid, there are some small ere. 

 taceou* bodies suspended by a beautiful plexus of 

 nerve*. These, in the osseous fishes, are three in num- 

 ber, and are hard and white like porcelain. In the 

 cartilaginous fishe* with free branchue, these bodies are 

 in general fewer in number, and of a softer consistence, 

 being ncldom harder than moistened starch. It is sup- 

 posed that these bodies assist in communicating to the 

 nerve* the vibrations produced in the water by sound. 



With the sac are connected three semicircular canals, 

 filled with a viscid fluid similar to that in the large sac. 



Stiucture 

 and 



The auditory nerves arise so near to the origin of f u jj ct i on * 



, -~ , . J . ot t-ishcs. 



uie nttn pair, that they have been considered as the _- _' 



same. In the genus Raja these pass into the cavity of 

 the ear by a particular foramen ; in the osseous fishes, 

 they are distributed directly into that organ. 



As the ear of fishes is much less complicated in its 

 structure than in the higher orders of animals, we may 

 conclude that the sense of hearing is weak in propor- 

 tion. Indeed the difficulty of detecting any natural 

 movements of fishes, occasioned by sound, led the an- 

 cients to conclude that they did not enjoy this sense. 

 We have, however, demonstrated its existence, but we 

 are unable to ascertain the advantages which these ani- 

 mals derive from it, or the influence which it exerts 

 on their habits and economy. In systematic ichthyo- 

 logy, the characters of the organs of hearing are too 

 minute and difficult of detection, ever to be employed. 

 They vary in different species, it is true, and may be 

 resorted to in cases of difficulty; but for their investiga- 

 tion they require a dexterous hand and an experienced- 

 eye. 



4. Organs of Taste. As the tongue of fishes (the Tasting. 

 organ in which the sense of taste resides in the higher 

 orders of animals) is but imperfectly developed, natu- 

 ralists are in general disposed to conclude, that the 

 sense of taste cart scarcely be said to belong to this class 



of beings. It presents no visible distinct papillae, and 

 its skin is analogous to the common integuments of the 

 mouth. The nerves which supply it, are branches of 

 the same nerves which proceed to the branchiae. In 

 the present state of our knowledge it is impossible for 

 us to assign the precise influence which the sense of 

 taste exercises on the economy of fishes. If noxious in- 

 gredients exist in the water, it appears probable, that 

 some warning will be given the animal of their pre- 

 sence, either by the nerves of the mouth during the 

 passage of the water to the gills, or by the latter or- 

 gans. It doea not appear that this sense is ever used 

 in the discrimination of food, and does not furnish any 

 characters, as such, to the systematic ichthyologist. 



5. Organt of Touch. We have already observed 

 that the skin of fishes is destitute of the corpus papil- 

 lare, and hence anatomists have concluded, that they 

 possess the sense of touch in a very limited degree. 

 Besides, few nerves have hitherto been traced to the v 

 skin ; and as its surface is in general coated with scales, 



it appears but ill adapted for receiving very delicate 

 impressions. In some species, such as the common 

 trout, ( .Va/iu fario,) the sense of touch is well dis- 

 played, if, under a stone or bank, the hand be mo- 

 ved gently towards it, and its sides titillated. It will 

 exhibit the pleasure it derives by leaning on the hand, 

 and if the operation be performed with care, every 

 part of the body may be gently stroked, and the fear- 

 less fish in part raised above the water. 



From these observations on the organs of sensation, 

 the reader will readily perceive that fishes hold a much 

 lower place in the chain of being than quadrupeds or 

 birds. The organs of smell and sight, appear to be 

 more completely developed than those of hearing, taste, 

 or touch, and therefore claim the attentive considera- 

 tion of the student in his enquiries after a natural me- 

 thod in ichthyology. 



Fishes possess no voice by which they can commu- 

 nicate their sensations to others. Some species utter 

 sounds when raised above the water, by expelling the air 

 through the gill opening when the flap is nearly closed. 



