I 74 
THE LIVING WORLD. 
OPHIDIA—SNAKES. 
In the natural sequence of changes produced by a gradual cooling of the 
earth, as already explained, land animals became more numerous as the waters 
receded, and following amphibious saurians, other creeping and no less repul¬ 
sive creatures appeared, adaptable to the modified temperature and conditions. 
Reptiles in this next order are classed by naturalists as Ophidia , a Greek word 
meaning serpent , and under this head therefore, must follow descriptions of all 
the numerous species, which have been divided by Lacepede into eight genera, 
each of which are again subdivided into several classes. The eight genera 
comprise the Boa , which contains 11 species; the Vipers , of which there are 
196 species; Rattlesnakes , with 26 species; Snakes (under which name the 
harmless find classification), 24 species; the Amphisbcena , a double-headed, 5 
species ; Lang rata, 1, Coecilia 2, and Acrocboid , 1. 
All true snakes, whether venomous or harmless, are clothed with a scaly 
skin which they shed at least once each year, and during this season they are 
irritable and sluggish, giving every indication that the change of skin is 
accompanied by more or less physical disturbance, if not actual pain. The 
old skin begins t.o peel first from the head, splitting on top and fleecing down 
over the eyes and then breaking in a line along the back. This dead integument 
sometimes comes off in perfect condition, and with the exception of a single 
rift along the back has all the appearance, save its transparency, of the snake 
itself, every scale, and even the delicate covering of the eyes having a most 
natural appearance. 
Legs, or even the rudiments of limbs, are wanting except in a few of the 
largest species, where a posterior protuberance, as in the Boa , is barely 
perceptible. Yet while possessing no limbs these reptiles move with astonishing 
ease and some few with very great celerity, whether on land or in water. 
Their movements are accomplished by the use of the scales upon the belly, 
called scutes. These scutes perform the service of legs, by which the creature 
can erect and firmly hold itself to any rough surface, and by using them 
consecutively drag itself along. All snakes, however, are unable to move 
forward over a perfectly smooth surface. To the strange provisions made to 
enable the serpent reptiles to travel, is added a wonderful formation of structure, 
by which the body is capable of remarkable recurvation and flexibility, due to 
the ball-joints of both ribs and vertebrae. 
The heart in reptiles is so constructed, that at each of its contractions 
only a portion of the blood which it receives is transmitted to the lungs, the 
remainder of this fluid is returned to circulate again, without having passed 
into the lungs and, consequently, without having been subject to respiration; 
hence it results that the action of oxygen on the blood is greatly less than 
in mammiferous animals and birds, where all the blood by passing through 
their lungs is exposed to the action of the air. Consequently, as respiration 
causes the heat in the blood and gives to the muscular fibre its susceptibility 
for nervous irritation, the temperature of reptiles is much lower,' and their 
muscular power greatly weaker than that of the mammalia and birds. There¬ 
fore they are said to be cold-blooded animals. Their general habits are also 
much less energetic, almost all their motions consisting of crawling and 
swimming, and although several species run or leap, at times with considerable 
facility, yet upon the whole their actions are sluggish. 
