8 PREFACE TO THE FIRST EDITION 



An appendix, giving some suggestions concerning laboratory and 

 field work, is added in response to numerous requests that have 

 come from teachers for such information. 



The author is very greatly indel^ted to INIiss Winona H. Welch, 

 Miss ]\Iargaret C. Jacobs, and INIr. W. C. Croxton, all of whom 

 have read the entire manuscript and have aided greatly in eliminat- 

 ing typographical errors, crudities in English and errors in the state- 

 ments of facts. All illustrations obtained from individuals or used 

 by permission of publishing companies are acknowledged in the 

 legends of the figures. Illustrations not so acknowledged are by 

 the author. Naturally, free use has been made of the published 

 statements of numerous ecologists for which individual acknowledge- 

 ment is not attempted. Sincere thanks are hereby exj^ressed to all 

 who have aided in any way, directly or indirectly, in the preparation 

 or publication of the book. 



W. B. McD. 

 Urbana, Illinois. 



