viii PREFACE 



As for the remainder of the illustrations, they are from my 

 own photographs and drawings, those of animals being based 

 for the most part on specimens in the collections of the Royal 

 Scottish Museum. The reproduction of this extensive series 

 of illustrations was made possible by a very generous grant 

 from the Trustees of the Carnegie Trust for the Universities 

 of Scotland. 



Most of all, the reader and myself are indebted to my 

 wife, Jessie J. Elliot, who has been associated with this 

 work from its beginning. She shared in the reading of old 

 books and records, has constantly been consulted during the 

 development of the theme, read a proof, and is responsible for 

 the full index. 



It ought to be added that the material in the pages which 

 follow was presented in lecture form to general audiences in 

 Aberdeen in December 191 7, as a course under the Thomson 

 Lectureship in Natural Science in the United Free Church 

 College. 



J. R. 



EDINBURGH, 

 March 1920. 



