FISHES. 
39 
however, are provided with tails. We therefore 
readily group the amphibians into two distinct orders. 
8 . “One thing I had almost forgotten to tell you. 
The skin of the amphibians is full of little holes, 
through which water finds its way in. Owing to 
this, in a manner I cannot now explain, the 
creatures of this class are able to stay for a long 
time under water before coming to the surface to 
fill their lungs with air.” 
FISHES.— I. 
1. The next time Arthur and William went to 
see Mr. Johnson, the afternoon was spent in a long 
talk about fishes. 
“ I have not many specimens to show you to- 
day,” said their friend; “though enough, I think, 
to make clear to you that fishes are very different 
in build and habits from the animals of other 
classes. 
2. “Here I have a very pretty skeleton of a bony 
fish, in which you may plainly see the long back- 
bone with its many joints. Every bone or vertebra 
of the backbone is hollowed out on each side, where 
it meets the next bone; and the rim of one hollow 
makes a joint with the rim of the next. In this 
way the backbone bends easily, and enables the fish 
to turn and twist in the water.” 
