REPTILES. 191 
They generally deposit their eggs in warm sandy places, 
leaving them to be hatched by the warmth of the atmos- 
phere. 
313. There are five orders of Reptiles: 1. The Turtles 
or Tortoises. 2. The Crocodiles. 3. The Lizards. 4. The 
Serpents. 5. The Amphibia. 
314. The Tortoises are unlike all other animals in their 
covering. They are in a fortified house of bone and horn, 
which they carry around with them. Into this they can 
wholly retire when attacked. In some of the Land Tur- 
tles this covering is so jointed that they can close the 
openings before and behind after drawing in the head, 
legs, and tail, thus shutting the doors of their portable 
house against their enemies. The construction of this 
covering is worthy of examination. It is composed of 
two shields, an upper and a lower one. The upper one, 
called the carapace, has a coating of plates of horn. As 
the turtle grows, each plate grows by enlargement around 
its edge. The tortoise-shell, so much used in making 
combs, comes from this coating in one species. On re- 
moving this, we see that the carapace is composed of a 
large number of plates of bone, very nicely and firmly 
joined together. There is a row of eight plates through 
the middle, and these are appendages of the vertebre of 
the back of the animal. These vertebre yoy see in Fig. 
6, where the lower shield is removed, so that you have a 
view of the under surface of the carapace. As the ribs 
extend from the vertebra they expand, thus making some 
of its side plates. The lower shield, called the plastron, 
is the same thing as the breast-bone of other animals, 
only it is enormously large. 
315. Life in these animals goes on at a low rate, and 
lasts a long time—in some cases even over two hundred 
years. Their sensibilities are dull, and it is very difficult 
to kill them, as they survive the severest injuries. They 
vary considerably in the form of their feet and of their 
shell, especially the former, according to their mode of 
