ANIMAL FORMS 



CHAPTEE I 



INTRODUCTION 



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1. Divisions of the subject. Biology is the science which 



treats of living things in all their relations. It is sub- 

 divided into Zoology, the science which deals with animals, 

 and Botany, which is concerned with plants. The field 

 covered by each of these branches is very extensive. 

 Within the scope of zoology are included all subjects bear- 

 ing on the form and structure of animals, on their devel- 

 opment, and on their activities, including the consideration 

 of their habits and the wider problems of their distribution 

 and their relations to one another. 



These various subjects are often conveniently grouped 

 under three heads : Morphology, which treats of the form 

 and structure or the anatomy of organisms ; Physiology, 

 which considers their activities ; and Ecology, which in- 

 cludes their relations one to another and to their surround- 

 ings. All the phases of plant or animal existence may be 

 considered under one or another of these three divisions. 



2. The difference between animals and plants. Generally 

 speaking, we have little difficulty in seeing that the objects 

 about us are either living or lifeless ; but the boundary line 

 between the two great divisions of living things, the animals 

 and plants, can not always be so clearly drawn. This is es- 

 pecially true of the simpler forms of life which frequently 

 combine both animal and plant characteristics ; but in the 



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