34 



ICHTHYOLOGY. 



lifted Iht fait mdly scientific work on Uiis subject. 

 which was followed by another by Hay in i;i:i. 

 Artedi considerably improved this branch of science, 

 but died before the completion of his work, which 

 was adopted by !.iim;ru- in his first edition of the 

 Sfftrma Nattira. Tossing over various successful 

 writers on Ichthyology, we come to the time of Lace- 

 pede, who publisned five quarto volumes on this sub- 

 ject, from 1798 to 1803 , hit it is to the celebrated 

 r that we are indebted for the most perfect 

 arrangement on fishes, and whose method we have 

 adopu.l. 



Fishes have red, cold blood, with cartilages or bones, 

 with fins instead of limbs, and which inspire and 

 expire air, in combination with water, by means of 

 gills, instead of lungs. They can live but a short 

 time out of the water, although eels have been seen 

 on land in fields of pease. At Tranquebar, there are 

 l>. red which, by means of the sharp points on their 

 fins, climb up the palm trees. (See the article Fin.) 

 According as fishes have cartilages, or a bony struc- 

 ture, they are divided into two general classes. 

 The cartilaginous fishes either have or have not a 

 gill-cover. To the latter kind belong the lamprey, 

 the ray, and the shark ; to the former, the sturgeon, 

 the porcupine-fish, the sea-needle, the eel, and the 

 sword-fish. The bony fishes are divided into orders, 

 according to the position of the ventral and thoracic 

 or pectoral fins. In the eel-pout, the Baltic dorse 

 and the haddock, the ventral fins are placed before 

 the pectoral ; they are directly under them in the 

 bream, the perch, the perch-pike, the mackerel, and 

 the river-perch, and behind them in the salmon, the 

 pike, the herring, and the carp. In the structure of 

 fishes, the fins are remarkable as being the only 

 organs of motion. (See Fint.) They consist of 

 bony rays, covered with the epidermis, and attached 

 to certain cartilages or bones which are moved by 

 particular muscles. The tail, with its fin, serves as 

 a rudder, to give the proper direction to the motions 

 of the animal. The first impulse in swimming evi- 

 dently comes from the tail ; the other fins serve to 

 regulate the position of the fish, and to guide him in 

 his different motions. The eel, which has no ventral 

 fins, swims like water-snakes, by moving his whole 

 body in an undulating manner. The muscles of 

 fishes must be distinguished from the fleshy muscles 

 of warm-blooded animals. They consist of white or 

 light coloured layers, with fibres of a thicker texture 

 Uian those of warm-blooded animals ; between these 

 layers there is a white, gelatinous substance, which 

 grows putrid very soon after death. If we look at 

 the organs of sense and the nervous system in fishes, 

 we cannot but remark the extraordinary smallness of 

 the brain in proportion to the size of the body. In 

 m;m, the brain is 1-23 of the body ; in the shark, 

 it is 1-2500, and in the tunny-fish, 1-37,400 ; it is also 

 less solid than in warm-blooded animals, and consists 

 mostly of lumps resembling ganglions. The cere- 

 bellum is only a transverse plate, entirely without 

 the structure, which, in higher orders of animals, 

 is called arbor vitae. The nerves of fishes are weaker 

 than those of the higher animals ; some of them, 

 Itowever, are such powerful exciters of electricity, that 

 they can give violent shocks ; but the power ceases 

 as soon as the nerves are cut. The torpedo, the 

 gymnotus, the electric eel, the Indian-needle, and 

 the electric porcupine fish, are five fishes which 

 appear to be living Voltaic piles ; for they have two 

 muscular piles, separated from each other by a mem- 

 brane resembling a net, and which, at least in the 

 torpedo, lie under the curved cartilages of the large 

 side fins, and are regulated by particular nerves. 

 As to the organs of sense in fishes, those of smelling 

 nd seeing appear o be the most perfect. Fishes 



smell the bait further than they can see it, and the 

 shark perceives ut an incredible distance the odour of 

 a Negro. Their organs of smell have no connexion 

 with those of respiration; and the water apparently 

 conveys the effluvia affecting the sense of smell much 

 less perfectly than the air ; but they have very large 

 olfactory nerves, the ends of which were for a long 

 while taken for the true brain. As to their organs 

 of sight, they have very large eyes, but generally no 

 eyelids ; but the epidermis goes directly over the. 

 eye, and in the blind-fish appears to have only ? 

 slight transparency. The cornea is very flat ; imme- 

 diately behind it usually is the crystalline, which can 

 protrude even through the pupil, so that there is very 

 little room for the aqueous humour. The crystalline 

 of fishes, on the other hand, is nearly spherical, and 

 also of a greater density than that of land animals : 

 it is apparently moved by an organ in the shape of a 

 fan, which proceeds from a knot of several optic 

 nerves. The iris is generally of extraordinary bril- 

 liancy, and of a beautiful red or gold colour ; the 

 vitreous humour is very small. The organs of hear- 

 ing are less perfect, although this sense cannot be 

 entirely denied to fishes. Only cartilaginous fishes 

 have an external auditory passage, as the shark and 

 the ray; the fishes with bones are without this 

 external ear. All of them have three winding tubes 

 in their head, which terminate in a bag filled with 

 nervous marrow, and containing three hard bones. 

 This constitutes the whole organ of hearing. That 

 of taste seems to be still more imperfect. Their 

 tongue has not even the papillae, and the nerves are 

 branches of those which go to the gills. The respir- 

 ation of fishes is carried on by means of their gills ; 

 these are well known to be vascular membranes, four 

 on each side, fastened to a curved and flexible 

 cartilage. They are connected with the carti- 

 lages of the tongue, and with the cranium. In car- 

 tilaginous fishes, the gills are within the body like 

 bags, and a determinate number of external openings 

 lead to them ; the lampreys, and that kind called the 

 nine eyes, have seven, rays and sharks five of these 

 openings. Several fishes have also a peculiar 

 covering for the gills, and frequently a membrane 

 over them, which can be contracted or extended. 

 It encloses a number of winding cartilages, which are 

 called its rays. The gills, as is very evident, can 

 only receive the air which is mixed with the water. 

 What is called the air-bladder is, in most fishes, 

 joined by an air-pipe, to the stomach or throat. This 

 is thought to contain nitrogen ; but it is certain that 

 it assists their rising in the water. Several fishes, as 

 the loach and gudgeon, breathe also through the 

 excretory duct, as is fully proved. The ling are even 

 discovered when at the bottom of the sea, by the 

 rising of air bubbles. Fishes commonly have no 

 voice; but the father-lasher, the loach, the trout, 

 and some others, give, when pressed, a murmuring 

 sound, in doing which they seem to make great ef- 

 forts, and tremble all over their body. It is very 

 prolble that this sound is produced by the aii, 

 violently pressed out of the bladder. The circulation 

 of the blood in fishes is. as might be expected, dif- 

 ferent from that of the higher class of animals. The 

 heart consists only of one auricle and one ventricle ; 

 it receives the blood from the body, and sends it, by 

 a single artery, directly to the gills ; it is here pro- 

 vided with oxygen by contact with water, and the 

 air contained in it, and is again received by a number 

 of small vessels, which flow together into the aorta, 

 which distributes the blood over the whole body. 

 The motion of the heart is, in fishes, much more 

 independent of the brain and spinal marrow than in 

 the higher orders, and, for this reason, can continue 

 several hours after the brain and spinal marrow have 



