" W^ fetM )&'€if( )&T€2( ^^ ^^^ !^^^ fe^ !^^ mjlrj 



PREFACE 



FOR more than thirty years the author has been 

 engaged in the study of the interrelationships of 

 the different forms of animal life. This study has 

 included both intensive research on the forms within 

 certain restricted groups, particularly the birds, in- 

 sects, onychophores, echinoderms and certain other 

 types of marine invertebrates, and extensive investiga- 

 tions concerning the relationships of all of the various 

 groups of animals each to the other. 



It has also included a detailed survey of the fossils 

 of the Cambrian, with the late Dr. Charles D. Wal- 

 cott, the Secretary of the Smithsonian Institution, and 

 more or less intensive investigations of other fossils, 

 especially the past representatives of the great group 

 of sea-lilies — the Crinoidea — in cooperation with the 

 late Mr. Frank Springer. 



Intensive laboratory work has been supplemented 

 by extensive field work in various parts of North 

 America, in South America, in the West Indies (par- 

 ticularly in the Lesser Antilles), in Europe, in eastern 

 Asia and Japan, and in the Aleutian and Hawaiian 

 Islands. 



Studies on land and along the sea coasts have been 

 broadened into detailed investigations of the animals of 

 the open ocean and of the sea bottom down to a depth 

 of 11,838 feet beneath the surface. These investi- 

 gations were carried out during the cruise of the 

 United States Bureau of Fisheries steamer Albatross in 



[vii] 



