VI PREFACE TO FOURTH EDITION 



Some new figures have been added in this edition, 

 and the work has been revised throughout. For advice 

 and help in the parts dealing with the Echinoderma and 

 the Polyzoa my thanks are due to Dr Bather and Mr 

 W. D. Lang ; and for various suggestions I am indebted 

 to Mr R. G. Carruthers, Mr G. C. Crick, Miss G. L. Elles, 

 Dr G. J. Hinde, Dr F. L. Kitchin, Mr P. Lake and other 

 friends. 



H. WOODS. 



May, 1909. 



