Reptiles (Reptilia). 
INTRODUCTION. 

weal LIE REPTILES form the third Class of 
{ il Vertebrated Animals. Whilst Mammals 
and Birds present such well-marked cha- 
racteristics that anyone would recognize 
a mammal or bird at once, this is not so easy in 
the small class of Reptiles, and it needed the pene- 
tration of true 
naturalists to arrange animals so 
different in shape and size in one Class. Of course 
this classification was not founded upon the external 
appearance of the animals but upon the characters 
of the internal organs. Thus all reptiles, whatever 
their form, are cold-blooded vertebrates, with lungs, 
but with the large and small circulatory systems im- 
perfectly separated. 
The Reptiles used formerly to be placed in 
one class with the Amphibia, partly on account of 
the similarity of their external appearance, and partly 
on account of their structure, although the latter is 
really very different. The skeleton shows transitions 
from a simple cartilaginous spinal column without ribs or 
limbs, to a complete bony vertebrate column with a 
larger or smaller number of long ribs, and strong and 
long extremities. The Reptiles, comprising the Tor- 
toises, Lizards, and Snakes, have only one articulation 
connecting the head with the first vertebra, but the 
Amphibia have two. 
The form of the body differs remarkably in 
different species. We meet with gradations from 
the long cylindrical Snakes, without, or with only 
rudimentary limbs, to the broad flattenned bodies and 
well-developed limbs of the Tortoises. 
Equally varied are the appendages of the skin. 
The Lizards and Snakes are clothed with scales, but 
Reptiles are divided into four Orders: 
Order I. Snakes. Ophidza. 
» Il. Crocodiles. Cvrocodilia. 
jaws provided with strong teeth. 
» Ul. Lizards. Lacertilia. 
jaws provided with sharp teeth. 
» IV. Tortoises and Turtles. Chelonza. 
(plastron); limbs four. 
beak of a bird. 

the young 

tortoises are encased in a coat of mail formed of 
plates of bone connected with the skeleton itself. 
The brain is small in comparison to the size 
of the body and of the spinal cord, and_ therefore 
the intelligence is rather limited, but the eyes, ears, 
and sense of smell are fairly well developed in most 
reptiles, though not always equally. Respiration 
is effected in all reptiles by means of large-celled 
lungs, in which the blood comes into far less com- 
plete contact with the air than in the case of mam- 
and birds. This is the cause of the lower 
temperature of their blood, which only rises a few 
mals 
degrees above that of the surrounding medium. It 
also explains the comparative sluggishness or muscu- 
lar inactivity of the whole Class. 
The heart consists of two separate auricles, 
with thin walls, and two larger ventricles, which are 
usually imperfectly separated. 
Reptiles differ as much in their habits as in 
outward form. Some live partly on land and partly 
in the water, whilst others live always on the land. 
On the whole the benefits and injuries which man 
derives from reptiles are fairly balanced; on the one 
hand many injurious or unpleasant animals are de- 
stroyed by reptiles but on the other hand they in- 
clude venomous snakes, boa constrictors, and croco- 
diles, which are themselves dangerous. 
The Eggs are covered by a calcareous parch- 
ment-like shell, and are generally buried in the 
ground, and left to be hatched by its warmth. Some 
snakes brood over their eggs with their body until 
many cases the young 
emerge from the eggs directly after they are laid; 
emerge. In 
and a few reptiles are viviparous. 
Body long and cylindrical without limbs. 
Body covered with thick bony plates; toes clawed and webbed, and 
Body covered with horny scales; limbs four, two, or absent; toes clawed; 
Body encased in a backplate (carapace) and a breastplate 
Teeth replaced by a sharp horny covering over the jaws, like the 
Amphibia. 
