276 Oil the Classification of Fishes. 



others only hj a smootli mucous skin, as some of the Catfishei. 

 The scales are of two kinds : one kind is composed of a substance 

 resembling horn ; the other is harder and quits enamel-like in its 

 appearance, and may be seen on the Garfishes. For the most part 

 iishes are oviparous, reproducing by eggs, and these usually are 

 fecundated after they are laid ; but the distinction between ovipa- 

 rous and viviparous animals has lost its importance since modern 

 science has shewn that there is a period in the existence of every 

 animal when it was enclosed in an egg. The limbs of fishes are 

 adapted in form to suit the element in which they move, so that 

 instead of arms and leg^ they have fins. Those on the back are 

 called dorsal fins; the one that forms the tail is the caudal fin ; the 

 fins on the under side, which are placed vertically, are called anal 

 fins ; the remainder are arranged in pairs, one fin on each side : 

 the pair nearest the head are called pectoral fins ; the other pair,, 

 usually placed behind the pectorals, though sometimes found just 

 beneath them, are the ventral fins. The number of dorsal and of 

 anal fins varies in difierent species, but there is never more than 

 one caudal, nor more than one pair of pectorals or of ventrals ; but 

 in some species the ventrals are absent, and in others the ventrals 

 and pectorals are both wanting. The fins are a membrane, usually 

 thin, supported and extended by rays. Some of these rays are- 

 composed of a single continuous bony spine, hard and often 

 sharply pointed, and these are called spinous rajs ; others are 

 formed of numerous small bones articulated upon each other, often- 

 branching out towards their extremities into several filaments^ 

 which, from their structure, are soft, and flexible, and are called 

 indifferently soft rays, flexible rays or articulated rays. Some fins- 

 are composed part of spinous rays and part soft rays, like the dor- 

 sal fin of the Hock Bass, Centrarchuscsncus ; some are wholly 

 spine-rayed, like the first dorsal of the American Sandre, Lucioperca 

 Americana ; and some are wholly soft-rayed, like the fins of the 

 common Pickerel, Esox reticidaius 



The teeth are usually a simple spine, very acute, and curving' 

 inward at the tip, and are arranged sometimes in single rows, 

 sometimes in double and sometimes in cards. They are to be met 

 with on the tongue, the vomer, the palatal bones, the maxillaries, 

 intermaxillaries, and on the pharangeal bones, and their presence 

 or absence is of much importance often in determining the species. 

 The vomer is the bone in the centre of the roof of the mouth ; 

 the palatal bones are those lying on each side of the vomer^ and 



