REPTILES. 
33 
plates, which fit together so as to form a kind of 
box in which the creature lives. The scales and 
plates must be a good protection when the reptiles 
move amongst the stones or fallen trees. 
6. “ Here is the backbone of a snake,” added Mr. 
Johnson. “ See how numerous are the bones in it, 
and how beautifully they fit so as to allow" them to 
turn upon each other. I think, after seeing this, 
Skeleton of a Snake. 
you can understand how it is that the snake bends 
its body so easily.” 
Mr. Johnson explained to the boys how the scales 
on the under part move with the ribs, and enable 
the snake to glide forward. 
7 . “ Like the animals in the first two classes, 
reptiles have lungs ; but I must tell you of an im- 
portant difference between the heart of a reptile 
and that of a mammal or a bird. A reptile’s heart 
has only three chambers — two upper and one lower. 
In consequence, the circulation of its blood is not 
so perfect as that of the creatures in the two higher 
classes, nor is the blood so warm. 
( M 387 ) 
C 
