Li B 



PREFACE 



THE lectures out of which this book has grown were 

 written for the author's students at the Woman's College of 

 Baltimore, and for others in the college not familiar with 

 biology who had expressed a desire to attend such a course 

 of lectures. The book is, therefore, not intended for biolo- 

 gists, but rather for those who would like a brief introductory 

 outline of this important phase of biological theory. 



It has been the author's endeavor to avoid technicality 

 so far as possible, and present the subject in a way that will 

 be intelligible to those unfamiliar with biological phenomena. 

 The subject, however, is somewhat intricate, and cannot be 

 presented in so simple a manner as to require no thought 

 on the reader's part ; but it is hoped that the interest of the 

 subject will make the few hours spent in the perusal of this 

 book a pleasure rather than a burden. 



In many instances matter that might have been elabo- 

 rated in the text has been treated in the pictures, which, with 

 their appended explanations, form an essential part of the 

 presentation of the subject. This method of treatment has 

 been chosen both for the sake of the greater vividness thus 

 secured and because it enables the book to be reduced to the 

 limits desired. Many of the illustrations have been obtained 

 from books with which the reader may wish later to become 

 familiar. 



In his lectures upon evolution the author made no 

 attempt to avoid following the manner of presentation or 

 even the phraseology of prominent writers upon the subject, 



VII 



