PREFACE 



Doctor Macbride's death occurred in Seattle, Washington, on March 

 27, 1934, after a short illness, just as the final copy for the present vol- 

 ume was being made ready for submission to the publishers. During 

 the six years it has been in preparation he has taken an active part in 

 the work, reading and criticising the manuscript and proofs, and mak- 

 ing numerous suggestions, based on his long familiarity and wide ex- 

 perience with the organisms of which it treats. Many of these sug- 

 gestions have been embodied in the treatment. It has been a privilege 

 to have been associated with him in the work; it is a satisfaction to 

 record in this place his uniform kindliness and courtesy, and the in- 

 spiration of his rare personality. 



In the very nature of the case, the task of which this is a part can 

 never be complete. This publication, like others of its kind, may 

 represent merely a milestone, marking, in so far as it is honestly and 

 competently wrought, a certain degree of progress toward adequate 

 understanding of the infinite variety of forms in which life has been 

 manifest. It is offered with a keen sense of its shortcomings and 

 limitations, but with the hope that in its turn it may serve as a new 

 starting point for further advance. 



Of the many who have shown helpful and sympathetic interest in 

 the undertaking, mention can be made of only a few. Dean C. E. Sea- 

 shore of the Graduate College of the University of Iowa has been 

 most generous in the provision of research assistance. The assist- 

 ants themselves, Dr. Frank L. Howard, Dr. H. C. Gilbert and 

 Mr. Donald P. Rogers, have rendered valuable aid at successive 

 stages. Upon Mr. Rogers, in particular, has fallen the burden of much 

 of the final detail, including the checking of citations, the reading of 

 proof and the preparation of the index. To his intelligent perception 

 and keen interest I am indebted for the detection of numerous errors. 

 Finally, I must acknowledge the devoted assistance of my wife, 

 rendered in many ways throughout the progress of the work. 



G. W. Martin. 

 Iowa City, Iowa, 

 March 31, 1934. 



