PREFACE. 



The following chapters were originally written in the form 

 of lectures, delivered first at Cornell University, where they 

 were supplemented by special laboratory work and illustrated 

 by actual specimens of the organisms or fossils described. The 

 attempt was made to replace the ordinary treatment of the 

 dry statistics of historical geology and paleontology by some- 

 thing which would bring the chief problems of the history of 

 organisms within the comprehension of the ordinary college 

 student, and kindle in the special student enthusiasm for 

 deeper research. In preparing them for publication the lec- 

 ture form was dropped, such revision of the language and 

 treatment was made as to provide for readers who might not 

 have at hand full museums from which to draw illustrative 

 material, and a few of the more characteristic examples, used 

 in elucidating the principles discussed, were selected and more 

 fully and precisely elaborated, so as to make a text-book for 

 use in earnest and exact study as well as an exposition of gen- 

 eral principles. 



Two classes of readers were considered in giving the book 

 its present form, viz., students in colleges and universities 

 who have begun to appreciate the importance of understanding 

 the principles of the nature and history of organisms, either 

 as a preparation for further special studies or as a part of a 

 liberal education ; and second, the general reader, who is sup- 

 posed to know something of the present popular theories re- 

 garding organic life, and has, perhaps, already become aware 

 of the increasing sense of disappointment which those are 

 meeting who have attempted seriously to apply them to the 

 solution of the problems of human life. It is not assumed 

 that the reader has any special knowledge of biology or geol- 

 ogy to start with. On this account some details have been 

 given which would be unnecessary for the specialist^ while, on 

 the other hand, many elaborations which would interest him 



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