Preface. vii 



in common. Thus he is enabled to distinguish groups. Memorized 

 definitions have comparatively little value. " A neat definition is a 

 very attractive thing. It seems to offer the sum and substance of 

 wisdom in portable form. But to understand it. to comprehend what 

 it includes and what it excludes, the thoughts of the master must be 

 gone over again in the mind of the disciple, and then he no longer 

 needs the definition." But definitions, however made, are often mis- 

 leading. The fact is that nature has not sharply and distinctly sepa- 

 rated animals into groups. There are usually no hard and fast lines 

 between them. If we try to establish a dividing line, we almost always 

 find it cutting across some intermediate forms. Since the groups of 

 animals overlap, and gradually shade off one into another, it is better 

 not to try to think of them as having definite boundary lines. We 

 should rather consider each group as arranged about a type at the 

 center. 



PRACTICAL WORK. It has been thought best to place the practical 

 work in the latter part of' the book. But this work should, of course, 

 precede the assignment of lessons in the descriptive text. Effort has 

 been made to correlate the two parts so that they may be used together 

 to good advantage. The author is well aware that in many schools the 

 facilities for field and laboratory work are very limited. He has, there- 

 fore, thought best to err on the safe side and give rather full descrip- 

 tions. But the teacher should see to it that the student himself solves 

 as many as possible of the problems. 



The teacher may find help in the " Suggestions to the Teacher of 

 Zoology,' 1 which is issued in pamphlet form by the publishers of this 

 book. 



ECONOMIC IMPORTANCE OF ANIMALS. The common schools aim 

 primarily at intellectual acquisition and training rather than at indus- 

 trial application. Still, the economic side of the study of animals 

 should be kept clearly in mind. The public has a right to demand 

 that the knowledge gained in school shall have some practical value. 

 The economic side, too. is one of the most interesting, and should 

 receive attention for this reason, if for no other. This is a line of work 

 in which collateral reading may be most profitably followed. There 

 are many Reports of the Department of Agriculture which may be 

 obtained free on application to the Department of Agriculture, Wash- 



