ANIMAL FORMS 
CHAPTER I 
INTRODUCTION 
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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