PISH: 



the internal lining of the mouth, which forms a sort of 

 valve ; and this valve also assists in conducting the 

 food towards the gullet, which is also promoted by 

 the teeth on the tongue and palate, which being 

 reflected or bent towards the opening of the gullet, 

 prevent any return. When it arrives at the pharynx, 

 or posterior part of the mouth, it, in most of the 

 species, meets with a third set of teeth on the pha- 

 ryngeal bones, by means of which it is conveyed into 

 the gullet. This canal is of very ample dimensions, 

 not much less than the whole capacity of the mouth ; 

 so that many fishes appear internally like a sack as 

 far down as the stomach. The gullet is abundantly 

 furnished with muscles, the action of which furthers 

 the progress of the food downwards ; and it is pos- 

 sible that in many instances the process of digestion, 

 or decomposition of the food, begins here, as it is 

 known to do in many of the reptiles. The stomach 

 of fishes is in general thin and membranous, differing 

 little in its structure and appearance from the gullet. 

 It frequently contains the remains of crustaceous 

 animals, still retaining their form, but greatly altered 

 in consistency. Hence naturalists have concluded, 

 that the food is reduced by solution, and not by 

 trituration. But in some fishes, particularly those 

 which subsist principally on shell-fish, the stomach has 

 thick muscular coats. Its shape is considerably 

 different in the different species, but the characters 

 furnished by this organ are seldom regarded. The 

 intestinal canal varies much in the different species. 

 In some it is straight, in others it has convolutions, 

 but it is never so long as in most of the mammalia. 

 In many bony fishes there are a sort of caecal append- 

 ages to the canal ; but it is in the cartilaginous fishes 

 only ; which, though by far the least perfect in the 

 ossification of their skeletons, are the most so in the 

 the other parts of their economy. The abdominal 

 viscera are enclosed in a membranous peritoneum, 

 which has small openings near the vent, by which any 

 liquid in the cavity of the body can be discharged, 

 but none can readily be admitted. The greater 

 number of fishes are, strictly speaking, monostomata, 

 or have only one vent or opening for all sorts of 

 discharges. 



One remarkable viscus in fishes, to which there is 

 nothing correspondent in any other of the vertebrated 

 animals, is the air-sac, or air-bladder, which some 

 have and some are without, and the rea,l use of 

 which in the economy of the animals is not known. 

 Some notice of this curious viscus will be found in 

 the article AIR-BAG ; but we shall not enlarge upon 

 it, as all that is known is that it cannot have the use 

 which is commonly supposed that of regulating the 

 specific gravity of the fish. If this bag were to be 

 alternately filled and emptied of air, according to 

 the different pressures of water to which the fish was 

 subjected at different depths, then, we must suppose 

 that the fish must have the means of filling it. A 

 " gas-work" in the cavity of a fish for this purpose, 

 is not likely, and besides there is no apparatus. 

 Neither is the air with which this muscle is filled, the 

 refuse of that from which the oxygen apart necessary 

 for the purposes of life, is taken in the process of 

 respiration ; for though the greater part of the con- 

 tents is nitrogen, the quantity of oxygen in it increases 

 as the fish to which it belongs is an inhabitant of 

 deeper water. As little can it be filled from the 

 external air when the fish is at the surface, because 

 its contents are not the same as the atmosphere ; and 



also if supplies were taken in there it would hinder the 

 descent of the fish. Besides, of fishes that have 

 similar habits, some of them surface fishes, and others 

 bottom or ground ones, some have this viscus, and 

 others are without it. Thus, the only conclusion to 

 which we can come in the present state of our know- 

 ledge is, that we are in utter ignorance as to its real 

 use. The air-bag of fishes, when cleared of fatty 

 matter, is perhaps the purest gelatine which is 

 obtained from the whole animal kingdom ; and as 

 such, it is of much value both as an article of food 

 and in the arts. 



Though we do not think it necessary, in this brief 

 outline, to give any account of those secretions of 

 the liver, the pancreas, and other viscera of fishes, 

 which assist in the assimilation of their food, and 

 in other parts of their economy, and which do not 

 appear to differ very essentially from the same pre- 

 cedents in other vertebrated animals ; yet there is 

 one peculiar secretion of the surface which is so 

 peculiar, that we cannot wholly pass it over in silence. 

 This is the secretion with which they are covered over, 

 and which appears to be the means by which their 

 bodies are preserved from injurious maceration by 

 the water in which they float, and by means of which 

 also, they are allowed to range thereon in whatever 

 direction may be necessary. 



The last of these is a matter of more consequence 

 than they who have not been in the habit of attend- 

 ing to such subject would readily suppose. Accord- 

 ing to a well-known law of bodies floating in water, 

 if that water were to wet them completely, they 

 would have a constant tendency to come on shore ; 

 and though, in the case of a fish, this might be occa- 

 sioned by perhaps not a very great deal of muscular 

 effort, yet that effort would be a continual one, and 

 would wear them out more than a greater effort 

 made only at intervals. The friction of the water in 

 the case of a wet fish, would also be a considerable 

 disadvantage, but the grand disadvantage, however, 

 would be the decomposition of the epidermis, and 

 the consequent pain and destruction of the whole 

 animal. All these bad effects are prevented by the 

 mucous secretion. 



As might be expected from their difference in 

 other respects, the production of this mucus is not 

 quite the same in the bony and the cartilaginous 

 fishes. The following account of it in the skate, by 

 the late Dr. Monro, will show how intimately it is 

 connected with even the most important part of the 

 system. " First," says Dr. Monro, " I have discovered 

 one very elegant serpentine canal between the skin 

 and muscles, at the sides of the fine apertures into the 

 gills. Further forwards it surrounds the nostrils ; 

 then it passes from the under to the upper part of the 

 upper jaw, where it runs backwards as far as the eyes. 

 From the principal part of this duct, in the under 

 side or belly of the fish, there are not above six or 

 eight outlets ; but from the upper part near the eyes, 

 there are upwards of thirty small ducts sent off, 

 which open upon the surface of the skin. The liquor 

 discharged from these has nearly the same degree of 

 viscidity as the synovia in man. But, besides the 

 very serpentining duct I have been describing, I have 

 remarked on each side of the fish, a little further 

 forwards than the fine breathing holes, a central part 

 from which a prodigious number of ducts issues, to 

 terminate on almost the whole surface of the skin, 

 excepting only on the snout or upper jaw. At these 



