PREFACE. 



MY aim in writing this work has been to give such an 

 account of the development of animal forms as may prove 

 useful both to students and to those engaged in embryo- 

 logical research. The present volume, save in the intro- 

 ductory chapters, is limited to a description of the develop- 

 ment of the Invertebrata : the second and concluding volume 

 will deal with the Yertebrata, and with the special histories 

 of the several organs. 



Since the work is, I believe, with the exception of a small 

 but useful volume by Packard, the first attempt to deal in a 

 complete manner with the whole science of Embryology in 

 its recent aspects, and since a large portion of the matter 

 contained in it is not to be found in the ordinary text 

 books, it appeared desirable to give unusually ample 

 references to original sources. I have accordingly placed 

 at the end of each chapter, or in some cases of each section 

 of a chapter, a list of the more important papers referring 

 to the subject dealt with. The papers in each list are 

 numbered continuously, and are referred to in the text by 

 their numbers. These lists are reprinted as an appendix 

 at the end of each volume. It will of course be understood 



B.E. B 



