PREFACE TO THE SECOND 

 EDITION 



Besides corrections, alterations, and smaller additions, the 

 book in its present form contains three new chapters, two 

 upon some parasites a knowledge of which is increasingly 

 important, and one upon cold-blooded vertebrates, which 

 it seemed desirable to include, for reasons stated in the 

 chapter itself. The greater part of the new matter has been 

 inserted with the object of increasing the value of the 

 work to medical students, though some of the paragraphs 

 have rather the purpose of indicating the relation of well- 

 known animals to those already described in detail. The 

 additions have been co-ordinated as thoroughly as possible 

 with the substance of the first edition, and have been 

 treated so as to bring into the foreground the generalisa- 

 tions of the science. Instructions for obtaining, observing, 

 and dissecting certain animals are added to the Appendix. 

 In writing these, and in preparing the illustrations of the 

 present as of the former edition, I have received the most 

 valuable and ungrudging assistance from Mr. W. Brockett, 

 Head Assistant in the Cambridge Zoological Laboratory. 

 Mr. Thornton Shiells has also placed me under obligation 

 by the care and skill which he has bestowed upon the 

 drawings from which most of the new figures have been 



