BU OG L.. 
Pruatrses 74-118. 
General Introduction. 
Zoo.oay is a systematic exposition of animals according to their external 
and internal structure, and the functions of their organs. The internal 
structure can be frequently inferred from the external characters ; we may, 
for example, determine the aliment of an animal, and the structure of the 
digestive organs, by examining the teeth. This is, however, not sufficient 
in all cases, so that it becomes necessary also to examine the internal parts, 
because the relation between animals depends upon the entire organization ; 
and this being well ascertained, the functions of the various organs can 
generally be determined without much difficulty. 
From the earliest period it was found necessary to group those animals 
together which were observed to have certain natural characters in common. 
We find, upon inquiry, that the endeavors to arrange animals systematically 
have taken two principal directions, which have been named natural and 
artificial classification. The former has in view the classification of animals 
upon the greater or less perfection of the various organs, among which 
those connected with the circulation and oxygenation of the blood, 
locomotion, and digestion, hold a prominent place; the latter depends upon 
a character or habit arbitrarily chosen, and independent of others. A 
character, however, which may be regarded as unessential by one observer, 
will be considered as of the greatest importance by another. In the earlier 
stages of science, when the number of known species was comparatively 
small, artificial methods were popular, because they were considered easy 
of acquisition: now, however, it is found that they are calculated to give 
superficial ideas ; and that to present the condition of zoological science in 
its true light, a more philosophical system must be made use of. 
Aristotle, whose great mind was master of many sciences, both moral and 
physical,-and whose works had an authority in Europe for many centuries, 
second only to that of the sacred Scriptures, takes precedence, in point of 
time, as the first systematic zoological observer. Born at Stagira, in the 
year 383 before Christ, he became the instructor of Alexander the Great, 
who formed a large collection of animals to enable him to pursue his investi- 
gations. As a history of zoological systems forms no part of the plan of 
this work, only a short outline of the most important periods will be 
given. 
ARISTOTLE divides animals into such as have blood, and such as are 
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