ZOOLOGY. 
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INTRODUCTION. 
OOLOGY means, in its widest sense, the study of 
animals. For the sake of convenience we may take 
as our unit of study either the whole animal kingdom, a 
single animal, or any intermediate group between these 
two extremes. Let us first take the animal, or individual 
organism, and notice how its study may be approached. 
We can inquire into the manner in which the organism 
is put together or constructed by an examination. of its 
external appearance and by a dissection of its interior. This 
study of structure is called MorpHotocy. It is often, 
though somewhat unnaturally, divided into ANaTomy or 
morphology of organs, and HisTroLocy or morphology of 
celis and tissues. Our real knowledge of an organism would, 
however, be very limited if we did not go on to inquire 
the meaning of its structure and howit works. This study 
of function is called PuysioLocy. Structure and function 
go hand in hand throughout the constitution of the 
organism, and it is impossible to study the one without 
due consideration of the other. 
The next important fact about an organism is its zz- 
constancy in structure and function. The organism passes 
through a definite sequence of changes from birth to death. 
The greatest and most obvious changes are those which 
occur during early life called development, and the study of 
these is termed EmBryOLocy. 
Embryology includes morphology and physiology of the 
young, or more rapidly changing, organism. ; 
In morphology, parts of an organism which have a 
similar structure and structural relationship to other parts 
are called homologous, whilst in physiology those parts which 
M. i. 2 
