x PREFACE 



of them for suggestions. I am under great obligations to 

 my artist?, and in particular to Mr. J. K. Maxwell, Mr. 

 Edwin Wilson, and Mr. M. P. Parker, by whom the majority 

 of the drawings were made. Professor J. Arthur Thomson 

 has kindly consented to my borrowing from his Outlines of 

 Zoology a large number of illustrations which are the 

 property of the publishers of this work. Messrs. Bell & 

 Sons, Messrs. Kegan Paul, Trench, Triibner, & Co., and 

 the Cambridge University Press have permitted me to 

 reproduce illustrations from works owned by them. My 

 acknowledgments to the authors of these works are made 

 in the legends of the figures. 



L. A. BORRADAILE. 



Sklwyn College, Cambridge, 

 September 1912. 



