REPTILES agree in having four distinct articulated members, a very small brain, no external ear, and no cochlea within the labyrinth, no distinction of thorax and abdomen, no epiglottis, no omentum, no mesenteric glands. Their heart, in most tribes, has two auricles ; their lungs are of course confounded with the other vis cera. They have two ovaries and two oviducts, and a common passage for the excrements and the ova, as in birds. Their bodies are covered neither with hair nor feathers.
The general differences that take place in the struc ture of reptiles, admit of their division into three or ders. In the first of these the heart has always two au ricles; the jaws are horny, hut without teeth, and the body is covered with a dorsal shell. These are chelo niens or chelonia of Cuvier. In the second order, the heart has two auricles, the jaws have teeth, but there is no dorsal shell. These are the sauriens or saurca of Cu vier. In the third order, the heart has only one auricle, the body is naked, and has in most instances four ex tremities. These are the batraciens, or batracea of the same author. See HERPETOLOGY.
The SERPENTS differ from the reptiles, in having a long body without articulated members, and commonly covered with scales, a heart constantly with one auricle, and in having both jaws moveable.
The general differences among this class arc so few, that it would be unnecessary, in the present article, to subdivide them. See OPHIOLOGY.
In FISHES the brain is extremely simple, and by no means fills the cavity of the skull; their car has no tym panum, and no external organs ; both their jaws are moveable ; their heart consists of one auricle and one ventricle ; they breathe by means of gills ; have neither wind-pipe nor larynx, and their nose is not connected with the organs of respiration. They have no pancre4s,
and no urinary bladder. The male has two testes, and female two ovaries.
The general differences in the structure of fishes, re spect either the consistence of their skeleton, or the position of their fins. From the former circumstance, they are divided into bony fishes, in which the skeleton is is bony ; and cartilaginous, in which it is gristly.
The cartilaginous fishes are distinguished according to the structure of their gills, into two orders; chontrop terigii, in which the gills are fixed, and have no cover ings; and branchiostegi, that have the gills free, and fur nished with covers. The bony fishes are distinguished according to the situation of their fins, into four orders. In the first there are no ventral fins, and these fishes arc called ?podes. In the second order, the ventral fins are immediately below the thoracic fins, and these are called thoracici; in the third order, the ventral fins are situated sacrad of the thoracic, these are the abdomi nales; and in the fourth, the ventral fins are atlantad of the thoracic, these are the jugurares.
As this arrangement is the same, both in the system of Cuvier, and in that of Linn as improved by Gmelin, it is unnecessary to repeat it in a tabular form. The na tural history of fishes will appear under ICHTHYO