ZOOLOGY. 



INTRODUCTION. 



ZOOLOGY 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 Morphology. It is often, 

 ttiough somewhat unnaturally, divided into Anatomy or 

 morphology of organs, and Histology or morphology of 

 cells 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 how it works. This study 

 of function is called Physiology. 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 i7i- 

 cofistancy 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 Embryology. 



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 



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