XVI INTRODUCTION. 
a web, and the central toe is often longer and stronger than 
the rest ; the hind toe is sometimes wanting. This order con- 
tains the ostrich family, the bustards and plovers ; the cranes, 
herons, and storks ; and the snipes and woodcocks. 
6 Palmipedes, or web-footed birds. These birds have the legs and 
feet short, and placed behind, with their fore toes united by 
a thick, and strong membrane. The neck is much longer 
than the legs, and their bodies are covered with a dense layer 
of down, beneath the outer plumage, which is close, and im- 
bued with an oily fluid that repels the water. The principal 
birds in this order are the coots and grebes, the auks and 
penguins, the petrels, the pelican and cormorant, and the 
swans, ducks, and geese. 
THE REPTILIA, 
Or Reptiles, have neither hair, wool, nor feathers, and their bodies 
are either naked, or covered with scales. Some lay eggs, and some 
bring forth their young alive. Some have gills, and others lungs, 
but the latter have only a portion of the blood passing through them ; 
and thus the blood of reptiles is cold, as it is respiration which gives 
the blood heat. The senses of reptiles are dull, and their move- 
ments are either slow or laborious. The following are the four 
orders into which this class is divided : 
1. Chelonian Reptiles. These animals have a heart with two auri- 
cles, and a body with four legs. The body is enclosed in an 
upper buckler, called the corapace, and an under one, called 
the plastron. They have lungs which are much expanded ; 
but they have no teeth, though they have hard horny 
jaws. The females lay eggs covered with a hard shell. 
The principal animals belonging to this division are the 
tortoises, which live on land, and the turtles, which are al- 
ways found in or near water. 
2. The Saurian Reptiles. These animals have also a heart with two 
auricles, expanded lungs, and generally four legs, but some 
have only two. Their bodies are covered with scales, and 
their mouths with teeth. This order includes all the croco- 
diles and lizards. The crocodiles have broad flat tongues, 
attached throughout to the jaws, and the lizards have long 
narrow tongues, which they 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 heart 
has two auricles, and the lungs are generally well developed. 
Serpents are frequently furnished with poison-bags at the 
base of their teeth. 
4. The Batrachian Reptiles include the frogs and toads. The heart 
has only one auricle, and the body is naked. The greater 
