. Cassell's natural history. Animals; Animal behavior. 14 XATURAL HISTORY. As a i-ule, there is a gall-bladder, but it is frequently absent; it is very small in the Rays, and is sometimes entirely separated from the liver, as in Lophius. The bile enters the small intestine near the stomach. The internal surface of the small intestine is usually smooth, but in the Herring it shows slight transverse folds, in the Sturgeon it is divided up into cells, and in the Sun-fish it is lined with little tubes called villi, which absorb the nutriment from the food. The large intestine is straight, and in t
. Cassell's natural history. Animals; Animal behavior. 14 XATURAL HISTORY. As a i-ule, there is a gall-bladder, but it is frequently absent; it is very small in the Rays, and is sometimes entirely separated from the liver, as in Lophius. The bile enters the small intestine near the stomach. The internal surface of the small intestine is usually smooth, but in the Herring it shows slight transverse folds, in the Sturgeon it is divided up into cells, and in the Sun-fish it is lined with little tubes called villi, which absorb the nutriment from the food. The large intestine is straight, and in the Ganoid fishes. Mud-fishes, Sharks, and Rays terminates in a remarkable spiral coil. Though the small intestine is coiled up spirally in the Sword-fish, the coils are not in contact, but in the cartilaginous fishes there is usually a spiral channel which winds around many times. In the Fox Shark there are thirty-four of these turns ; at the end of the intestine the membrane lining the valve is deeply honey-combed. Evidence of its existence in fossil fishes is found in the spirally-formed coprolites or petrified fseces which are met with in many of the geological formations. The organs for purifying the blood, by separating from it the waste products, are difierent from the kidneys of higher animals, and correspond to organs which exist only in the embryo, and are known to anatomists as Wolflian bodies. Their function, however, is the same in fishes as that of kidneys in other animals. In most bony fishes the kidneys are long and narrow, and extend along the abdomen firmly attached to the vertebra. The tissue forming them is usually of a reddish tinge ; it is soft and spong}', and supplied with arteries from the abdominal aorta, which form the minute globular secreting organs termed Malpighian capsules, similar to those which abound in the outer layer of the kidney in liigher vertebrates. Sometimes two ureters lead from the kidney and enter a urinary bladder, but occasionally,
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