PREFACE vii 



ject of animal classification, it will be found that the system 

 adopted here is in accord with the general conception of the 

 relationships of animals held by scientists to-day. To the 

 beginner the classification of animals appears a well-nigh hope- 

 less, interminable task, and for this reason it has seemed best 

 to retain such types as the Vermes and the Arthropoda, desig- 

 nating their chief subdivisions as subtypes, while explaining 

 that the latter are more of the nature of types ; in this way a 

 certain unity, artificial, it is true, is maintained amongst the 

 very diverse representatives of the invertebrates, and this, I 

 believe, is of notable assistance to the elementary student with- 

 out leaving him with an erroneous conception of their general 

 relationships. 



While this portion of the subject is apt to be treated in a 

 way that is dry and unattractive to the beginner, my purpose 

 has been to introduce, whenever practicable, interesting facts 

 concerning such phenomena as commensalism, symbiosis, and 

 parasitism, the transmission of malaria and yellow fever by 

 mosquitoes, the cause of trichinosis and filariasis, and such 

 interesting habits as the division of labor in colonies and the 

 storing of food for the young. These are matters which the 

 general student especially wishes to know, and of which many 

 who undertake to specialize are often ignorant. 



The third portion of the book deals with the general prin- 

 ciples of zoology. As is well known, many German text-books 

 discuss these principles before they take up the special groups 

 of animals about which the generalizations are made — a 

 method which seems to many like putting the cart before the 

 horse. When the student is, to some extent, familiar with the 

 different kinds of animals, he is ready to consider such subjects. 

 Here is taken up first the distribution of animals, palaeontologi- 

 cally and geographically, then an outline of the various theories 

 of evolution is given, followed by a review of our knowledge of 

 the behavior of animals, considered, to some extent, psychologi- 

 cally; with, finally, a brief history of the science of zoology. 

 The definitions of the different branches of the biological 

 sciences have been placed in an appendix. 



The laboratory method is now the accepted method of instruc- 



