PISCES. 
291 
brane. In their eyes, the cornea is flat, and there is a little aqueous humour, hut 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 coeca 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 
forth the young alive. 
The proper classification of Fishes is a very difficult matter. There are two distinct 
series of them; — Fishes, properly so called, or Bony Fishes ; and Cartilaginous 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. 
Selachii (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 Ordinary 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 Plecto- 
GNATHi (soldered jaws), and they consist of two families : Gymnodontes (naked teeth), 
and Sclerodermi (hard skins). Another order, the Lophobranchii, which consists 
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