Another subject of curiosity is, The Respiration in Fishes. - Fish derive air from the water which they are inac-cessantly swallowing through the mouth, and throwing out by the gills. The gills are formed with infinite skill, and may be called a delicate kind of sieve, adapted for separating air from water. Their operation proves the radical difference between these two elements, and leads to the conclusion, that they are not joined Dined even when mixed. The gills are placed in the back part of the sides of the head, and are contained in a cavity adapted for them. They are a kind of red and flexible leaflets, consisting of a row of thin plates, like the blade of a knife, pressed against each other, and forming a succession of barbs or fringed substances, similar to those on the side of a goose-quill. These gills are covered with a small lid, and with a membrane, supported by cartilaginous threads. Both are capable of being raised and lowered; and, by being thus opened, they afford a passage to the water swallowed by the animal. A prodigious number of muscles give motion to these minute particles. It may appear almost incredible, that the number of particles connected with the respiration of the carp is not fewer than 4386. Of these, sixty-nine are muscles; while the arteries of the gills, in addition to eight principal branches, throw forth 4320 smaller ramifications, while each of the latter gives birth to a number of cross arteries. Add to this, that the quantity of nerves is not smaller than that of the arteries; and that the veins are divided and subdivided, like the arteries, inasmuch as they do not give rise to any transverse capillary vessels. In this manner the blood flowing from the heart of the fish is spread over all the plates or blades of which the gills are composed; so that a very small quantity of blood is exposed to the action of the water, for the purpose, no doubt, that each part may be easily penetrated by the particles of air detached from the water.

It is not easy to explain in what manlier these particles are detached from the water by the operation of the gills; but there seems no doubt of the fact, nor of the redness of the gills being a consequence of the operation of the air. That redness is exactly similar to the vermilion of the blood in the veins of animals with lungs, a vermilion considerably brighter than that of the arteries.