X INTRODUCTION. 
naked, or have their skin covered with warts. Many of the species 
shed their skins at certain times of the year. Several of them are 
furnished with a poison, which they eject into wounds that are 
made by their teeth. They chiefly live in retired, watery, and 
marshy places ; and, for the most part, feed on other animals, 
though some of them eat water-plants, and many feed on garbage 
and filth. None of these species chew their food ; they swallow it 
whole, and digest it very slowly. 
The offspring of all these animals are produced from eggs, which, 
after they have been deposited by the parent animals in a proper 
place, are hatched by the heat of the sun. The eggs of some of 
the species are covered with a shell ; those of others have a soft and 
tough skin or covering, not much unlike wet parchment ; and the 
eggs of several are perfectly gelatinous. In those few that produce 
their offspring alive, as the vipers, and some other serpents, the eggs 
are regularly formed, but are hatched within the bodies of the 
females. 
This class Linnaeus divided into two Orders. 
ORDERS OF AMPHIBIA. 
I. REPTILES. Havingfour legs, and walking with a crawling pace, 
as the tortoises, frogs and lizards. 
II. SERPENTS. Having no legs, but crawling on the body 
Fishes constituted Linnseus's fifth class of animals. They are all 
inhabitants of the water, in which they move by certain organs 
called fins. These, when situated on the back, are called dorsal 
fins ; when on the sides, behind the gills, they have the name of 
pectoral fins ; when below the body, near the head, they are ven- 
tral ; when behind the vent, they are anal ; and that which forms 
the tail is called the caudal fin. Fishes breathe by gills, which, in 
most of the species, are situated at the sides of the head. In some 
of the flat-fish, however, as the skate and thornback, they are on 
the under-part of the body. Fish rise and sink in the water, gene- 
rally by a kind of bladder in the interior of their body, called an 
air-bladder. Some of them, as the skate and other flat-fish, do not 
possess this organ, and consequently are seldom found but at the 
