AN ELEMENTARY 

 TEXT-BOOK OP BIOLOGY, 



PART II. ANIMAL MORPHOLOGY AND PHYSIOLOGY. 



INTRODUCTION. 



1. ZOOLOGY, the branch of Biology which deals with animals, 

 is such an immense subject that, like Botany, it is conveniently 

 split up into a number of subdivisions. The most important of 

 these are (1) Animal Morphology, dealing with the structure 

 and form of animals; (2) Animal Physiology, which treats of 

 their actions or functions; (3) Development, the application of 

 morphology and physiology to the study of immature forms ; 

 (4) Classification or arrangement; (5) Distribution, in space and 

 time; and (6) Phylogeny, the province of which is to make out 

 the past history of animal groups (phyla). We are mainly con- 

 cerned in this volume with the first three branches, and, to a 

 much smaller degree, with the questions of classification. 



The range of these subdivisions will be comprehended more 

 clearly if we consider what questions they seek to answer in 

 regard to some particular animal, say, for example, the common 

 Frog. 



(1) Morphology takes note of the external characters, such as 

 shape, colour, divisions of the body, &c., and by means of dissec- 

 tion determines that various systems of organs (digestive, &c., &c.) 

 are present, which have a definite arrangement, and which can 

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