PREFACE TO THE FOURTH EDITION. 



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 the previous 

 edition I had throughout the able assistance of Miss 

 Marion Newbigin, D.Sc., to whom the chapter on 

 Comparative Physiology is also due. I have also been 

 aided by suggestions from various kindly critics, especially 

 Professor W. C. M'Intosh, Dr. Ramsay Traquair, Dr. 

 John Beard, Mr. J. G. Goodchild, Dr. Arthur Masterman, 

 and Dr. John Rennie. 



Many new figures have been added, and I wish to 

 express my thanks to my artist friends, Mr. William Smith, 

 Miss Florence Newbigin, and Mr. George Davidson, for 

 the carefulness with which they have done their work. 



