NOTE TO THE SIXTH EDITION. 



THE alterations and additions which have been made in 

 this edition are the work of Mr. J. T. Cunningham, M.A. 

 The Supplement which he had added in the Fifth Edition 

 has now been incorporated in the body of the work, and 

 Part IY. Invertebrata has been rearranged so that the 

 types follow in general the descending order in classifica- 

 tion, beginning with the Crayfish and ending with the 

 Protozoa. 



An important addition has been made to Chapter XXII. , 

 on the Theory of Evolution, which was formerly very short 

 aiid inadequate. Mr. Cunningham has summarised as far 

 as space would allow the various facts and theories which 

 are considered of most importance by modern biologists 

 in relation to the problems of evolution. 



