PREFACE TO THE SIXTH EDITION 
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THis book is intended to serve as a Manual which 
students of Zoology may use in the lecture room, museum, 
and laboratory, and as an accompaniment to several well- 
known works, cited in the Appendix, most of which follow 
other modes of treatment. 
To numerous authorities I acknowledge an: obvious 
indebtedness, a detailed recognition of which would be 
out of place in a book of this kind. I must, however, 
acknowledge that in the preparation of a previous edition 
I had throughout the able assistance of Miss Marion 
Newbigin, D.Sc., and I have also been aided by sugges- 
tions from various kindly critics, especially Professor 
W. C. M‘Intosh, Professor P. J. White, the late Dr. 
Ramsay Traquair, Dr. John Beard, the late Mr. J. G. 
Goodchild, Dr. Arthur Masterman, Dr. John Rennie, 
Dr. W. D. Henderson, Mr. E. S. Russell, Mr. W. P. 
Pycraft, Mr. C. Tate Regan, and Professor H. J. Fleure. 
For most of the figures I am indebted to my artist 
friends, Mr. William Smith, Miss Florence Newbigin, 
