Introduction. xv 
2. The Saurian Reptiles. These animals have also expanded lungs, 
and generally four legs, but some have only two. Their bodies 
are covered with scales, and their mouths filled with teeth. 
This order includes all the crocodiles and lizards. The croco- 
diles have broad flat tongues, attached throughout to the jaws, 
and the lizards have long narrow tongues, which many of them 
can extend to a great distance from the mouth. 
3. The Ophidian Reptiles are the snakes and serpents. The body is 
covered with scales, but it is destitute of feet. The lungs are 
generally well developed, only on one side. Serpents are fre- 
quently furnished with poison-bags at the base of some of their 
teeth. 
4. The Batrachian Reptiles include the frogs and toads. The body is 
naked. The greater part of these reptiles undergo a transition 
from a fish-like tadpole furnished with gills to a four-legged 
animal with lungs. Others never lose their gills, though they 
acquire lungs, and of this kind are the siren and the proteus. 
THE PISCES, 
Or Fishes, are denned by Cuvier to be vertebrated animals with red 
blood, breathing through the medium of water by means of their 
branchiae or gills. To this definition may be added, that fishes have 
no neck, and that the body generally tapers from the head to the tail; 
that most of the species are furnished with air-bladders which enable 
them to swim ; and that their bodies are generally covered with scales. 
The heart has only one auricle, and the blood is cold. The gills re- 
quire to be kept moist to enable the fish to breathe, and as soon as 
they become dry, the fish dies. Thus fishes with large gill openings 
die almost as soon as they are taken out of the water ; while those 
with very small openings, like the eel, live a long time. Fishes have 
no feet, but are furnished with fins. The scientific knowledge of 
Fishes is called Ichthyology. Fishes are first divided into two great 
series, viz. the Bony Fishes, and the Cartilaginous Fishes, and these 
are again subdivided into nine orders, as follows :— 
Osseous or Bony Fishes. 
1. Acanthopterygii, or fishes with hard fins. 
2. Malacopterygii abdominales, or scft-finned fishes, with the ventral fins 
Ion the abdomen behind the pectorals. 
Malacopterygii sub-brachiati, or soft-finned fishes, with the ventral 
fins under the gills. 
Malacopterygii apodes, or soft-finned fishes, without ventral fins. 
Lophobranchii, or fishes with tufted gills. 
ClIONDROPTERYGII, OR CARTILAGINOUS FlSHES. 
Cyclostomi, or fishes with jaws fixed in an immovable ring, and with 
holes for the gills. 
Selachii, or fishes with movable jaws and holes for the gills. 
Sturiones, with the branchiae in the usual form. 
