146 NEW ZEALAND NATURE-STUDY BOOK 
IX.—VERTEBRATE ANIMALS. 
INTRODUCTION.—The Vertebrates, or backboned animals, we 
have seen, are divided into five classes, viz.— 
Fish ; Birds ; 
Amphibians ; /Mamimals. 
. Reptiles ; 
~ We shall now proceed to examine these in detail selecting 
typical examples of each class, with the view of discovering their 
\ distinguishing characteristics, and of learning something of their 
habits. 
THE FISH. 
Shape. The typical fish, such as Mullet or Kahawai, is 
shaped like a boat, tapering both to the head and tail. The 
wedge-shaped head enables the fish to cut through the water 
with ease and the tapering tail prevents, to a very large 
extent, a retarding “swirl” from taking place in the liquid 
as the animal moves along. There is no neck, the head 
being united directly with the body, which unlike that of 
most other vertebrates, is not distinctly marked off from 
but passes gradually into the tail. The broadest, thickest 
and hence heaviest part of the fish is the shoulder, which is 
usually situated back from the head and nearer the head 
than the tail: it is in fact from this thickened region that 
the fish tapers both fore and aft, and its position tends to 
keep the head in the proper direction during rapid move- 
ment through the water. 
TYPICAL FISH. 
Scales. The body of the fish is ‘covered with hard 
slimy cartilaginous overlapping scales, each scale having 
a fixed end towards the head and a free end towards 
the tail. This arrangement causes the scales to he 
close to the body whilst the animal is swimming 
and hence increases the ease of locomotion. The slimy 
covering serves the twofold object of lessening the friction 
