CARTILAGINOUS FISHES are those fishes which have a skeleton destitute of bony fibers. In some of these fishes, the skeleton is merely rudimentary, so that they seem to form an intermediate link between vertebrate and invertebrate animals. In the lance lets (q.v.), (amphioxus), it consists of nothing more than a slender, transparent, flexible dorsal column; in myxine also it is a soft flexible tube, without appearance of vertebra?, or of ribs; in the lampreys, the dorsal column is still a mere cylinder of cartilage, with out any notable division into segments; whilst even in the sturgeon, the center of the backbone is a continuous gelatinous cord, and in the sharks the vertebrae are formed of hollow cones, meeting at their apexes in the 'middle, and having their cups filled with the remains of the gelatinous cord, an arrangement from which result great elasticity and flexibility. In many instances, even in the higher C. F., several vertcbrw are united in a single piece; in all of them the skull is formed of a single piece without sutures, although the general form agrees with that of the skull of other fishes, and the same parts or regions may be recognized. The calcareous matter present in the skeleton is always deposited in a granular manner, giving a characteristic dotted appearance; but even in the skull of the basking shark, one of the most highly organized, the earthy matter has been found to form little more than 3 per cent of the whole substance; in the skeleton of the lamprey, it is only per cent. In other parts of their organization, C. F. differ from each other very widely; some of them possessing the organs of the senses in as great perfection as any fishes whatever, whilst in others these organs are very imperfectly developed. Linnaeus placed the C. F. along with batrachian reptiles in his class amphibia. By the general consent of naturalists, however, they are placed in the class of fishes. Cuvier, referring to the very different degrees of organization which they exhibit, says "they form a series ranging parallel to the bony fishes just as the marsupial marninalia range parallel with the other ordinary niammalia." Owen and
others, admitting the justice of this view, have, however, pointed out in the C. F. gen erally, characters corresponding with those of the osseous fishes in their embryotic state, and with the permanent or mature conditions which prevailed among the fishes of some of the older geological periods. One remarkable characteristic even of the higher groups of C. F.—sturgeons, sharks, rays, etc.—is the heterocercal tail, the vertebral column being prolonged into the upper portion of the caudal fin, and the lower one given off on its under side, as in the fossil fishes generally of the old red sandstone and other oldest fish producing rocks. Cuvier divided C. F., or chondropterygii (Gr. cartilage-finned) into 3 orders: sturiones (sturgeon, chimera, etc.), having the gills free, and gill-openings with a lid, like the osseous fishes: sclachii (sharks and rays), having the gills fixed. and con sisting of folds of membrane on a plane surface, with numerous gill-openings, the jaws movable as in other fishes generally; and cyclostomi (lampreys, etc.), also having fixed gills and numerous gill-openings, the mouth adapted for sucking. Muller and Owen, however, separate the cyclostomi of Cuvier from the other C. F., on account of important anatomical differences, particularly in the structure of the heart, which in the cyclostomi wants the bulbus arteriosua, or thick muscular swelling of the commencement of the arterial system close to the ventricle; whilst this, which may, in fact, be considered as a third chamber of the heart, is present in the sturiones and selachii, and within it, are 3 or more longitudinal rows of valves; characters derived from the vascular system being deemed by these great naturalists of the highest value in determining the arrangement. of the class of fishes. The lancelets occupy a place by themselves, from their absolutely wanting a heart, and having the circulation carried on by the muscularity of the entire vascular system.