PREFACE v 



of the chapters on Some of the Life Processes (Chapter XII), 

 on Living Matter : Protoplasm and the Cell (Chapter XIII), 

 and on Heredity and Evolution (Chapter XVII). For a 

 course planned to occupy less than a full year the authors 

 recommend the omission in their entirety or in part of the 

 chapters on The Dragon Flies (Odonata) and the May Flies 

 (Ephemerida) (Chapter III), The Spiders and Allies : Arach- 

 nida (Chapter XIV), Allies of the Acephala: Mollusca 

 (Chapter XIX), Allies of the Earthworms : Annelida (Chap- 

 ter XXII), and The Bath Sponge and Some Allies : Porifera 

 (Chapter XXVI). By deleting some of these chapters from 

 the invertebrate section, the teacher may gain time for the 

 consideration of some of the vertebrates. 



Before entering upon the work of the current revision the 

 authors secured the cooperation of representative teachers 

 who have been using the textbook. More than a hundred 

 biology teachers responded with personal letters and inter- 

 views concerning the details of the proposed revision. This 

 list of our colleagues, who in innumerable ways have aided in 

 the course of the preparation of the revisipn, is too long for 

 detailed acknowledgment here. The detailed criticisms and 

 suggestions offered by Miss Helen Loomis of the Bowen 

 High School, Chicago, Illinois, and by Dr. W. H. D. Meier 

 of the State Normal School, Framingham, Massachusetts, 

 have been of great value in directing the course of the revi- 

 sion. Dr. T. H. Frison of the Illinois State Natural History 

 Survey has very generously aided in numerous details, 

 especially in the verification of entomological terms. Bernice 

 F. Van Cleave, by constant collaboration in selecting and 

 in rewriting material, has been in great measure responsible 

 for whatever merit the new material may possess. As an 

 experienced biology teacher in secondary schools her aid 

 in maintaining proper perspective and point of view has been 

 inestimable. 



