A WALK WITH THE NATURALIST. 
11 
“ And neither the snail nor the dog has wings, 
like the bee,” added Arthur. 
“Ah!” said Mr. Johnson; “there is a much 
greater difference. I see I must put you right. 
Rover has bones and the other two crea- 
tures have not. That is the chief differ- 
ence that I want you to notice now. 
10. “ What I wish you to see is that 
the animal kingdom is made up of two 
great divisions. In one division we have 
animals with backbones, and in the other 
are all the animals without backbones. 
11. “Of all the bones in the body the 
most important is 
the spine or back- 
bone. It is not a 
single bone, as you 
might at first think 
from its name, but it 
is made up of a num- 
ber of little bones, 
called vertebra. 
These are fastened into one another in such a way 
that the whole backbone can be curved or bent. In 
your own backbone there are thirty-three of them. 
12. “ As every animal with bones must have a 
backbone, and as this is made up of little vertebrae, 
we call animals with bones Vertebrates, and those 
without them Invertebrates. 
The Spine, 
or Backbone, 
in Man. 
Top View of a Single Vertebra. 
