riscES. 



291 



brane. In their eyes, the cornea is flat, and there is a little aqueous humour, but the 

 crystalline lens is almost spherical, and very hard. The ear is a sac, in which are sus- 

 pended small hard bodies ; and there are three membranous canals within the cranium 

 in ordinary fishes, but in its walls in the cartilaginous ones. They want the Eustachian 

 tube and tympanal bones ; and only the Sharks and Rays have an external opening, 

 which in them is level with the head. As great part of the tongue is bony, and as it is 

 often furnished with teeth and other hard parts, Fishes can have little sense of taste. 

 The fleshy cirri, or beards as they are termed, of some of the species, are perhaps 

 organs of touch. The body is in general covered with scales, and generally speaking 

 they have no organ of prehension except the mouth. 



In most fishes, the intermaxillary bone forms the edge of the upper jaw, having the 

 maxillary or the labial behind it. The palatal bones, pterogoid and zygomatic pro- 

 cesses, and the tympanum and squamosa, form an anterior jaw, as in Birds and Serpents, 

 to the posterior part of which the lower jaw is articulated, which jaw has generally 

 two bones in each side, except in the cartilaginous fishes. The teeth are very various 

 in situation, in number, and in form. They are found on the intermaxillaries, the max- 

 illaries, the lower jaw, the vomer, the palate, the tongue, the gill-arches, and even on 

 the bones of the pharynx behind these ; [but many fishes have them only on some of 

 these places, and there are some which are almost, if not altogether, toothless] . 



Besides the gill-arches, the hyoid bone supports the gill-membrane. The gill-lids, or 

 operculi [by the working of which respiration is carried on] , consist of three pieces, the 

 operculum, sub-operculum, and inter-operculum. These are articulated on the temporal 

 bone, and play on the pre-operculum; but many of the cartilaginous species want them. 



The stomach and intestines differ greatly ; and, except in cartilaginous fishes, the 

 pancreas is supplied by cceca round the pylorus, or by a duplicature of the intestine. 

 The kidneys are against the spine, but the bladder is above the rectum, and opens behind 

 the vent and the reproductive passage, contrary to what is found in the Mammalia. The 

 male organs are large glands termed milts, and the female are sacs, which also attain 

 great size, and have the eggs in their internal folds. In most fishes, there is no im- 

 pregnation till after the expulsion of the eggs ; but in the Sharks and Rays, and some 

 others, the case is different, some of them producing perfect eggs, and others bringing 

 fortli the young alive. 



The proper classification of Fishes is a very difficult matter. There are two distinct 

 series of them: — Fisues, properly so called, or Bony Fishes ; and Cartilmjinous Fishes, 

 or Chondropterygii. The latter want some bones of the jaws, and have other pecu- 

 liarities : they are divided into three orders ; — 



Cyclostomi (round-mouths, or suckers), which have the jaws soldered into a sort of 

 ring, and numerous gill-openings. 



Selacuii (Sharks and Rays), which have gill-openings similar to the former, but 

 the jaws not soldered into a ring. 



Sturiones (Sturgeons), which have the gill-openings with a lid, as in the Fishes 

 properly so called. 



Of the Oiuiinary Fishes, or those with bones in the skeleton, one order have the 

 maxillary bone and the palatal arch fixed to the cranium. These are called I'i.iuto- 

 gn'athi (soldered jaws), and they consist of two families: GymnodonteM (naked teeth), 



and Sclerodermi (hard skins). Another order, the Lophoiskani mi, which c-iiM-ts 



u 2 



