Page:The American Cyclopædia (1879) Volume VII.djvu/245

 FISHES 237 even in advance of the pectorals, to the origin of the tail. The vertical fins serve the purposes of keel and rudder, and are the dorsal on the back, the anal under the tail, and the caudal at the end of the body. All these fins vary in size and in the number of rays which sustain them, being sometimes spiny, sometimes soft, branched, and composed of many small joints. In the old system of nomenclature, the mala- copterygians are bony fishes with soft articula- ted fin rays; the acanthopterygians, bony fish- es in which some of the rays are spiny ; and the chondropterygians, the so-called cartilaginous fishes. These classes have been variously sub- divided, and the reader is referred to the arti- cle ICHTHYOLOGY for the numerous classifica- tions from Artedi to Agassiz. The anus may open far behind the ventrals, move forward with them, and in their absence be situated even under the throat, as in sternarchm ; the jaws may be armed with different kinds of teeth, which often exist also on the tongue and various parts of the mouth and throat ; the lips may be provided with sensitive barbels as in the horn pout, or with fleshy appendages as in the sea raven (hemitripterus). The skin may be nearly naked or covered with very small scales ; the scales may be rough grains as in the sharks, thick plates as in the sturgeon, a smooth enamelled coat of mail as in the lepi- dosteus, smooth as in the herring, or serrated as in the perch. Along the side of the body is the lateral line, formed by a series of pores, the outlets of the muciparous glands ; this line ex- tends from the head to the caudal fin, general- ly at the mid height of the body, nearer the back in some fishes than in others, sometimes ceasing long before the region of the tail, and occasionally multiple ; the scales along this line are arched, notched, or perforated for the pro- tection of the ducts ; they are sometimes larger or smaller than the rest, and may be the only ones present ; they often have strange forms and armatures. In various parts of the body, but especially about the head, are numerous pores, or water tubes, by which water is intro- duced into the system, even into the circula- tion ; some are situated along the lateral line. The tissue of the fish skeleton is either carti- lage, fibro-cartilage, or bone ; the first is found in the sharks and rays, the second in the sun- fish (orthagoriscus) and angler (lophius), and the last in common fishes; the chemical composi- tion is that of other vertebrates, principally the phosphate and carbonate of lime. The oste- ology of the head, branchial apparatus, trunk, and limbs has been already given as fully as the limits of this work will allow, in the article COMPAEATIVE ANATOMY (vol. V., p. 173) ; for further details see Cuvier and Valenciennes, vol. i., and Owen on " Fishes." Most fishes are quick in their movements; the salmon, for instance, can swim at the rate of 40 ft. in a sec- ond, and can with ease pass over 20 to 25 m. in an hour ; progression is effected by lateral strokes of the water by the alternate flexions of the tail and trunk ; the manner in which the vertebrae are connected allows easy motion of the spine from side to side, and the muscles destined to move it are so largely developed as to form the principal bulk of the body ; while the vertical fins increase the amount of oar-like surface for purposes of locomotion, the pecto- rals and ventrals keep the fish in an upright position, and assist in directing its course ; the movements of the gill covers, by forcing back- ward the water which is passing between them, contribute to propel the fish forward. In the pipe fish (syngnathus) the dorsal fin in its vi- bration resembles that of the screw of a steam propeller, and, with a similar action of the tail, causes a forward or backward motion without any apparent movement of the body ; the nice adjustment of the movements of the fins of the pickerel, so that while every ray seems in ac- tion the fish is perfectly stationary, must have been noticed by every angler. The movements of fishes in a vertical direction are greatly as- sisted by the swimming or air bladder, which, though anatomically a rudimentary lung, by the air which it secretes enables those that have it to rise or fall in the water by compression or extension exercised by the ribs ; it is placed in the abdomen under the spine, and communi- cates often with the oesophagus or stomach ; the air is a product of secretion, and its contain- ing reservoir is sometimes a shut sac ; it is often, wanting in some species of a genus when others possess it, and is generally very small or absent in ground fishes, such as skates and turbots ; in some cases it is considerably vascular, resem- bling very much a pulmonary sac. The muscles of fishes are generally pale and comparatively soft, divided into parallel layers by aponeu- rotic laminae ; the flavor and odor are very dif- ferent from those of flesh, and the gases of de- composition are much more fetid. Some fishes have a singular apparatus by which they adhere to other bodies, animate or inanimate ; in the remora, of the genus echeneis, there is a flat- tened disk on the top of the head, composed of movable cartilaginous plates, by which it fixes itself to stones or the bodies of other fish- es ; in the lump fish and other discoboli, the ventrals are arranged to act as suckers for at- taching them to various substances; the lam- prey eel (petromyzori) also attaches itself by the mouth to stones and fishes. Eeferring the reader to COMPAEATIVE ANATOMY for details on the nervous system, the organs of sense, the scales, and the digestive apparatus, only gen- eral points of interest need be mentioned here. The cavity of the skull is very small compared to the size of the body, and the brain is far from filling it, a considerable space being oc- cupied by a spongy fatty substance ; the lobes are placed one behind the other in the follow- ing order from before backward: olfactory or lobes of smell, the cerebral hemispheres, the optic or lobes of vision, and the cerebellum. From the scaly covering of their skin, the sense of touch must be obtuse, and the lips are their