UfiNERAL Characters. REPTILES. General Characters 3 
climates. One general inherent condition for the mnl- 
tiplication of reptiles is the reunion of equatorial heat 
with moisture. It is in the immense and submerged 
savannahs or in the depths of virgin forests, in tropical 
countries, that these creatures most abound. Hence 
we find them in such vast abundance under the ardent 
sky of the Moluccas, in the isles of Sunda and of New 
Guinea, where they are the terror of the human race. 
Guiana too, and the intertropical parts of Africa and 
Fi; 
America, demonstrate to us the fact, that it is in the 
countries near the equator that reptiles are most 
numerous and most largely developed in size. 
The class Reptiles {EepHlia), according to Cuvier 
and many other naturalists, contains the Batrachians, 
that is, frogs, toads, newts, salamanders, (S:c., as well 
as lizards, serpents, crocodiles, and tortoises. The 
most recent systematic zoologists, however, are now 
agreed to constitute the Batrachians into a distinct 
2. 
Iclithyosauriis iiitermudius. — Oonyteare. 
class, under the name of Amphibia* or Batrachia 
and in the following pages we shall adopt this arrange- 
ment : — 
The class Reptiles, then, thus limited, may be 
defined — cold and red-blooded vertebrated animals, 
with a heart trilocular, that is, formed of three cavities, 
which consist of two auricles and one ventricle ; pos- 
sessing true lungs, the respiration being exclusively 
pulmonary throughout life ; having a hard and dry 
integument, which is generally covered with broad 
plates or imbricated scales; oviparous, the young, that 
is to say, being produced from eggs, which are depo- 
sited by the mother in such situations as to be hatched 
by the rays of the sun. 
When we say that Reptiles have cold blood, we mean 
that their natural temperature is not much, if at all, 
above that of the atmosphere or water in which they 
live ; that their power of producing animal heat is so 
limited as scarcely to be appreciable, and therefore not 
sufficient to prevent the system being immediately 
affected by the lowering of the temperature of the 
medium by which they are surrounded. In cor se- 
quence of this, we find that in our climate, and in 
countries where the temperature is low, they undergo 
a state of torpidity in some sheltered retreat, to which 
as a refuge instinct directs them, and where they remain 
during the continuance of winter. The mode in which 
the blood is circulated is ore of the principal charac- 
• Awpliibios having a double life. 
+ Batrnchos a frog 
teristics of reptiles. The heart — which consists of three 
cavities, viz., of two distinct auricles opening into one 
common ventricle — transmits at each contraction only 
a portion of the blood through the lungs, the rest being 
sent directly to the other parts of tire body, without 
being specially subjected to the influence of the respira- 
tory organs ; thus differing from the higher classes of 
animals. Mammalia and Birds, in which the whole of 
the blood must pass through the lungs before it is sent 
back to the more distant parts of the circulating system. 
The routine of the circulation is this : the right auricle 
receives the vitiated blood sent from the different parts 
of the body by the veins ; the left auricle the arterialized 
blood returned from the lungs ; and both auricles convey 
their contents into the cavity of the ventricle. These 
two kinds of blood are in this ventricle mixed together, 
and part of this mixed fluid is sent through the aorta, 
or great arterial trunk, to supply the system, and pail 
through the pulmonary arteries, to undergo a further 
degree of oxygenation in the lungs. “ It is clear then,” 
says Mr. Bell, “ that the blood is by this mechanism 
but partially changed by the action of oxygen ; in other 
words, that the quantity of respiration, speaking with 
reference to the physiological meaning of the term, is 
comparatively small. Hence arises the circumstance 
that these animals have what is called cold blood ; for, 
as it is from respiration that the blood derives its heat, 
and the temperature of the body is thereby sustained in 
animals which have more perfect respiration, it follows 
th.'it where this function is but imperhctly performed 
