2 INTRODUCTION 



istry, Physics, and Astronomy are Physical Sciences; while Zoology, 

 Botany, and Physiology are Biological Sciences. In its narrower 

 sense, the term Biology includes Zoology, Botany, and the closely 

 related sciences that deal with particular phases of animal and 

 plant life. In its broader sense, the term may include everything 

 related to Uving organisms and their activities. The division of 

 the sciences into a physical and a biological group is arbitrary. 

 Even the Social Sciences may be grouped as " biological," if we 

 choose to regard them as such, because they are concerned with the 

 activities of living beings. The Hst of Biological Sciences is. there- 

 fore, extensive; and what, if anything, is to be excluded depends 

 upon the point of view of the person making the classification. 



Zoological Science. — Biology is, therefore, the science of Uving 

 things, both plant and animal. Botany is the science of plants. 

 Zoology is the science of animals. The term Animal Biology, 

 which is sometimes used, means the study of animals as living 

 forms illustrating the principles often common to both plant and 

 animal life, rather than the principles related to animals alone. 

 The term Plant Biology might be similarly appUed, but has not 

 come into general usage. The accompanying table (p. 3) indi- 

 cates the larger groupings of problems and subject matter within 

 the field of zoological science. It should be studied in connection 

 with the definitions that follow. If the reader understands the 

 justification for the groupings thus exhibited, he has mastered the 

 definitions and their application. 



Forfn and Function. — The science of Morphology, which 

 deals with the structure of animal bodies, may be considered inde- 

 pendently, although it is really inseparable from Physiology, 

 which deals with their functions. Gross morphology, as studied 

 in the dissection of the human body by medical students or in the 

 dissection of the bodies of animals by students of Zoology, is com- 

 monly called Anatomy. Embryology has Hkewise its morpho- 

 logical and physiological aspects. The problem of form and 

 function further includes microscopic organization and activities. 

 Histology deals with the more general features of microscopic 

 structure, the forms of the living units or cells, and their arrange- 

 ment in tissues and in organs. Cytology deals with the internal 

 structure of cells in their finer details. Like Anatomy and Embry- 

 ology, Histology and Cytology began principally with descrip- 

 tions of structure, but they have become increasingly physiological 



