viil PREFACE TO THE SECOND EDITION 



made. I am indebted to Mr. M. A. Husain for a figure 

 of the mandible of the crayfish, to Professor J. Arthur 

 Thomson for permission to make a further borrowing 

 of illustrations from his excellent text-book, and to Pro- 

 fessor Nuttall for several figures. 



I have to acknowledge permission to reproduce illustra- 

 tions granted me by Methuen & Co. Ltd., Macmillan & 

 Co. Ltd., Cambridge University Press, George Allen & 

 Unwin Ltd., Blackwood & Sons, A. & C. Black Ltd., 

 and John Murray. Acknowledgment to the authors of 

 the works from which these figures have been taken is 

 made in the usual way in the legends of the figures. 



L. A. BORRADAILE. 



Sblwyn College, Cambridge, 

 September 1918. 



