02 CLASS III REPTILES. ORDERS I. AND 11. 



have two auricles to the heart, but only one ventricle : into 

 the left auricle, the red blood from the lungs is poured, and 

 into the right, the black blood from the body. From the au- 

 ricles, the two kinds of blood are immediately transferred to 

 the ventricle, where they are mixed together ; and this min- 

 gled mass is, by the contraction of the ventricle, sent through 

 two distinct vessels, in part to the lungs, and in part to the 

 body. 



/The vessels of reptiles, then, are not filled with pure red 

 blood, like those of the Mammalia and Birds, but with an im- 

 perfect fluid, not so well adapted to give them a high degree 

 of life and vigor. Hence, as the animal heat is always in 

 proportion to the quantity of respiration, they are cold-blooded. 

 Their lungs are not so large ; their circulation is slower ; 

 they consume less air, and are capable of living for a longer 

 time without it. They are, in general, sluggish and indo- 

 lent in their habits of life, obtuse in their sensations, and 

 slow in their digestion. In cold countries, they pass the 

 greater part of the winter in a dormant state. Their brain is 

 small, and their nervous system imperfect and of less influ- 

 ence than in the preceding classes. They produce their 

 young by means of eggs, but take no pains themselves to 

 hatch them. They have less intelligence, fewer faculties, 

 and less instinct, than either quadrupeds or birds. They are 

 arranged in four orders, viz. 



I. Chelonia, the Tortoises, are distinguished by the pecu- 

 liar structure of their ribs, sternum, and vertebrae. These 

 are so arranged as to form a complete covering, consisting of 

 an upper and under shell, joined together at their sides, which 

 permits only their head, tail, and four extremities, to be ex- 

 tended without it. The upper shell is formed by the exten- 

 sion and enlargement of the ribs and part of the back-bone ; 

 and the lower shell, by an alteration in the form of the ster- 

 num. Their other bones are not essentially different from 

 those of other vertebral animals. Thus a part of their skeleton 

 is, in fact, on the outside of their bodies. They have no teeth ; 

 but their jaws are armed with a tough, horny substance, which 

 supplies their place. Their stomach is simple and strong ; 

 their intestines are long, and they are capable of going a 

 great length of time without food. All the various species of 

 the turtle and tortoise belong to this order. 



II. Sauria, the Lizards. This order includes a very con- 

 siderable variety, and is composed of the crocodile, the alli- 

 gator, the chameleon, the true lizards, and the dragons. The 



