INTRODUCTION. 
REPTILES AND BATRACHIANS. 
The Reptiles and Batrachians belong to what are commonly called the 
Cold-blooded Vertebrates. This name is applied because the heat-pro- 
ducing capacity of their bodies is so low as to render them very susceptible 
to thermal variation in the surrounding air or water, and unable to main- 
tain any standard temperature. In Batrachia that breathe by means of 
gills, the small amount of heat the body is capable of producing is limited 
by the amount of oxygen in the water. A heart in which ventricles or 
atria are more or less incompletely separated mixes venous with the 
arterial blood supplied the tissues of lung-bearing Reptiles and Batrachi- 
ans; and thus, in consequence of partial oxygenation, their heat-producing 
capacity is reduced. Animals of these classes are, to a considerable 
extent, dependent on external heat; they are more active during the 
warmer portions of the season or of the day. During the winter of the 
temperate zones or the dry season of the tropics they are comparatively 
inactive. 
The Turtles, Crocodiles, Lizards, Amphisbaenians, and Snakes are Rep- 
tiles. They are hatched or born with the shape of the adult, breathe by 
lungs, and generally are covered by a skin the outer layers of which are 
folded so as to resemble scales. The Batrachians include such as the 
Toads, Frogs, Salamanders, Newts, Sirens, and Cvecilians. _ Nearly all of 
them breathe and progress like fishes during the earlier portion of their 
existence, and the majority go through a metamorphosis, taking on the 
form of the adult and breathing by lungs later in life. They are without 
the scale-like folds of the Epiderm. 
From the Turtles to the Snakes of the one, and from the Frogs to the 
worm-like Cvecilians of the other of these classes, there is a great diversity 
of forms and habits. In all the intelligence is of a low order. Commonly 
one or more of the senses is feebly or not at all developed. Many are slow 
in growth, and live to great ages. Most are tenacious of life, and able to 
do without food or drink for long periods. The greater portion are harm- 
less; the exceptions are such as the Crocodiles, the few venomous, and a 
