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 Vertebrata, 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 that they do not profess to 

 form a complete bibliography of the subject. 



B. II. B 



