16 NATURAL HISTORY. 



though they are wanting in Lampreys. They are always formed of flexible rays, which are generally 

 branched. The first ray is sometimes strong and spiny, and among Siluroid fishes is barbed on one 

 or both sides. In the Flying-fish, the Tunny family, and the Rays the pectoral fin attains its greatest 

 development, and is usually pointed; but, as Swainson has remarked, families which live in rivers and 

 lakes have the pectoral fins rounded. The Gurnards have the pectorals greatly developed, but their fins 

 are nearly always rounded, though they may be partially cleft or digitate; when broad at the base they 

 usually extend under the throat. The cleft fins are seen in the genus Cephalacanthus; the digitated 

 pectorals ai-e seen in the Gurnards. The pectoral fins of Sharks are generally large. In the Flat-fish they 

 are smaller than in any other member of the class. In the family Pediculati, or Fish Frogs, the pectoral 

 fins perform the office of feet. The ventral fins are less important in swimming than the pectoral ; they 

 are generally of small size, though in the genus Zeus they are larger. In the Eel group they are entirely 

 absent. The position of these fins varies, being placed under the throat in the Star-gazer ( Uranoscopus), 

 while in the genus Polypterus they are near the base of the caudal fin. When the pectoral is rounded 

 the ventral is usually rounded too, though this correspondence between the fins is by no means 

 universal. Some fishes possess fins which are capable of adhesion by suction. The family Gobiesocidre 

 has circular concave discs on the breast and belly, which extend between the pectoral and ventral 

 fins. In the genus Regalecus, or Ribbon Fish, the ventral fins have the rays broadened at the 

 extremity so as to resemble oars. The dorsal fin is rarely altogether wanting, though it is absent 

 from Gymnotus branchiurus. The dorsal fin is generally composed of a number of bony rays, placed 

 successively behind each other and connected by a membrane. Frequently there are two dorsal fins. 

 In the soft-finned group the hinder dorsal fin is generally formed of fat. The Polypterus offers a 

 remarkable type of dorsal fin, in that the fin is divided into a large number of finlets, which reach 

 from the head backwards. The dorsal fins are very thick in cartilaginous fishes, and are thinner in 

 the spiny-finned osseous fishes. A few genera have three dorsal fins, as may be seen in the Cods. The 

 rays forming the fin are sometimes slender bones, are sometimes jointed, and sometimes branched. 

 The branched spines are well seen in genera allied to the Mackerel. The common Stickleback 

 furnishes a familiar example of the spiny modification of the fin. Sometimes the dorsal fins are 

 triangular, and sometimes they are broad, and occasionally end in filaments. In a good many fishes, 

 especially among the Eels, the dorsal fin unites with the caudal fin. The anal fin corresponds more or 

 lass to the dorsal, only it is placed longitudinally on the inferior margin of the body, behind the vent. 

 Sometimes, as in Gymnotus, it extends nearly the whole length of the fish. The caudal fin is the 

 great organ of motion; it usually consists of two symmetrical lobes, which are made up of a number of 

 radiating rays. The terminal part of the notochord, or spinal column, as the case may be, bends 

 upward, so that a larger number of the fin rays lie below than above it; hence, although the tail in the 

 bony fishes is homocercal in form, it is heterocercal or unsymmetrical in structure. In the Tunny the 

 fin rays are attached to the sides of a somewhat fan-shaped terminal bone, and in these fishes the tail 

 h more deeply forked than in any other. The caudal fin presents every modification in form ; it is 

 lanceolate in the Indian Gobies, but is sometimes rounded, or truncate, oblong-oval, even, and variously 

 forked. Occasionally the caudal fin is indistinct ; it is but little developed in the Rays, and there is 

 no terminal fin in the Pipe-fish or in Chimtera. In one genus the fin is placed vertically upon 

 the extremity of the tail. The analogy of fins to wings is evidenced by their p3rforming the office of 

 wings in the Flying-fishes. One of the best characters by which the genera and species of fishes may 

 be identified and defined is furnished by the number of rays in the several fins. In most cases 

 these are written in formulse, in which the number of rays in a fin follows its initial letter. 



All fishes have the sexes distinct. The male organs constitute the well-known soft roe, while 

 the ovary of the female is hard roe. In the female the oviduct has its outlet usually in front of 

 the urethra, and behind the anus. In the Californian genus Ditrema the young reach a relatively 

 large size, and are packed in the body of the parent as close as Herrings in a barrel. The oviparous 

 cartilaginous fishes are remarkable for the large size of the egg, and the strength of the case in 

 which it is contained. In Sharks of the genus Cestracion this egg-case is spiral ; and in the 

 southern Chinuera it has an oval form with a fringed margin. The males of Chimseroid fishes 

 and Plagiostomes are armed with remarkable organs termed claspers, which are attached to the 

 bases of the ventral fins. A few fishes build nests. 



