PREFACE 



In common with the other books of this series, this 

 little volume seeks to meet the needs of two classes of 

 readers. It is intended in the first place as a supplemen- 

 tary reading book for students in elementary biological 

 courses; and, secondly, for those members of the reading 

 public who are interested in a simple, untechnical account 

 of some of the most wonderful of the processes of life. 



One-half of life, whether we are thinking of the life of 

 man or of the lower animals, is that devoted to the build- 

 ing up of successful individuals, and to adjusting these 

 suitably to the demands of their surroundings; the other 

 half has to do with perpetuating the species. These are 

 the two great problems of living things. Both are essen- 

 tial to permanence of life at any level. This book does 

 not undertake to discuss the first of these problems. It 

 tries to develop in a continuous way, as the text-book 

 cannot do, the story of how plants and animals produce 

 and care for their children. In this way the student can 

 get a better sense of the progress made from the lower to 

 the higher organisms, a more adequate idea of the evolu- 

 tion and perfection of the methods of reproduction. 



Furthermore, it is more and more becoming the convic- 

 tion of thoughtful students of education that our young 

 people must come to know and appreciate the meanings 

 of these great functions in human life. Most of them also 

 agree that this instruction, wherever it is given, in home 

 or in school, must be related to and imbedded in the larger 

 body of knowledge of which it is a part. It should not be 

 isolated or emphasized in such a way as to heighten sex- 

 consciousness or to produce shock and uneasiness. The 

 treatment in this book is intended to be such that the 

 whole organic story becomes a background by means of 



