PREFACE. 



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 Introduction, most of which follow other 

 modes of treatment. The volume is, in great part, a re- 

 edition ,of manuscript notes which I have sometimes cir- 

 culated among my students in order to facilitate both their 

 work and mine. Considering the limited size and purpose 

 of the book, I have seldom thought it necessary to cite the 

 authorities from whose works the facts have been obtained. 

 To these authorities, especially to those cited in the 

 " Notes on Books," I acknowledge my indebtedness. I 

 desire also to record my obligations to three friends, to Mr. 

 G. S. Corstorphine, B.Sc, for his revision of the proof- 

 sheets and for the index, to Mr. Norman Wyld, for most of 

 the chapter on physiology, and to Mr. William Smith, for 

 the care he has taken in drawing the illustrations. 



School of Medicine, 



Edinburgh, January 1892. 



