Vlll 



PREFACE 



the animal and vegetable kingdoms, and to discover its true in- 

 terpretation in terms of ontogeny, phylogeny, and chronology. 



The next division of the volume comprises papers on the 

 structure and development of Trilobita. The following section 

 presents developmental studies on the Brachiopoda. It should 

 be stated that this work was undertaken largely in the hope 

 that the results would lead to the principles governing a natural 

 classification of all forms in these two classes. In the brachio- 

 pods nothing further than a division into orders and a grouping 

 of the families under the orders was attempted. The elabora- 

 tion of this classification has been very fully carried out by 

 Mr. Charles Schuchert, in his " Synopsis of American Brachiop- 

 oda." For the Trilobita, a new arrangement into orders was 

 suggested, together with a redefining of the families and a 

 grouping of the genera under them. 



In the last division are three papers on special problems of 

 development. 



The author is greatly indebted to Miss Lucy P. Bush for 

 assistance in arranging the material for this volume, and 

 especially for aid while it was being printed. 



YALE UNIVERSITY, April 3, 1901. 



