viii PREFACE 



the source has been acknowledged. The blocks for 

 the illustrations have been prepared with great care 

 by Messrs. Walker & Boutall. 



In preparing this book I have received valuable 

 assistance from Mr. W. E. Hoyle, Dr. C. H. Hurst, 

 Professors Hickson and Herdman, and Mr. W. 

 Garstang. I must also thank Mr. Francis Dar- 

 win for permission to reproduce the extracts in 

 Lecture VIII. 



C. F. M. 



London, October 1894. 



