INTRODUCTION 3 



more general questions constitute what may be called theo- 

 retical Zoology, or the principles of Zoology. 



4. Practical Exercises. — The student may select ten or more kinds of animals 

 with which he is partially acquainted, and, from his observation and experience, 

 enumerate the points at which they touch human welfare. Are they, in each 

 instance, to be classed as helpful? as harmful? or merely as apparently indifferent? 

 Is their influence upon man's interest direct or indirect? 



What animals have, in the past, most appealed to your interest? Select that 

 particular quality in which you have been most interested (structure, beauty, 

 powers, instincts, habits) and show how the attempt to study or explain any one 

 takes you at once into all the others. 



5. Divisions of the Science. — The facts and principles 

 which have been, and are yet to be, discovered concerning 

 animals are so numerous and various in their bearings, and in- 

 vestigators approach the subject from such different points of 

 view that it is necessary, in order to express these results, to 

 divide zoology into several branches or departments. It must 

 be held in mind, however, that these divisions are more or less 

 artificial, and that the facts of each department are to be con- 

 sidered in connection with those of all the others, if they are 

 really to be understood. With all its departments, animal life 

 is to be thought of as a whole. Structures exist for the per- 

 formance of function, and the activities are valuable as they 

 adjust the animal to its whole life-relation. 



6. Morphology is the branch of the science which deals 

 with form or structure in its broadest sense, whether internal 

 or external, partial or total. In its most general meaning it em- 

 braces the study of animals from the standpoint of symmetry, 

 — that is, the form of the organism with reference to certain 

 planes passing through the body. For example, the human 

 body may be so divided by a single plane that two essentially 

 similar parts result, — the right and the left. Again similar 

 parts may succeed each other in a linear series, as in the seg- 

 ments of the earth-worm; or they may radiate from a central 

 point, as in the arms of the star-fish. This is the most funda- 

 mental kind of morphology. It relates the organism to position 

 and motion in space. It is called Promorphology, and is related 

 to Zoology somewhat as the study of crystals is to Mineralogy, 



Anatomy is that department of morphology which treats 



