INTRODUCTION. 
ZOOLOGY is that branch of Natural History which treats of ani- 
mals, and it embraces not only their structure and functions, their 
habits, instincts, and usefulness to mankind, but their names and 
systematic arrangement. 
Various systems have been proposed by different naturalists for 
the scientific arrangement of the animal kingdom, but that of 
Cuvier, with some modifications by Lamarck and Latreille, is now 
thought the best, and a sketch of it will be found under the head 
of Modern System in this Introduction. As, however, the system 
of Linnaeus was formerly in general use, and is still often referred 
to, it has been thought advisable to give a sketch of it first ; that the 
student may be aware of the difference between the old system and 
the new one. 
LINN^AN SYSTEM. 
ACCORDING to the system of Linnaeus, the objects comprehended 
within the animal kingdom were divided into six classes: Mammalia 
or Mammiferous Animals, Birds, Amphibia, or Amphibious Ani- 
mals. Fishes, Insects, and Worms, which were thus distinguished : 
CLASSES. 
C Hnf RinnH /Viviparous I. MAMMALIA. 
( With vertebrae? \ Oviparous II. BIRDS. 
f With vertebrae^ c With lungs 111. AMPHIBIA. 
Cold red Blood With gill! IV. FISHRS. 
(Without vertebra, Cold white Bloal{ ft* - y V ; $ 
