PEEFACE TO THE FOURTH EDITION 



ONLY a few changes have been made in the text of the last 

 edition. Of these, those most worthy of mention are (1) the 

 incorporation of Prof. Jennings' most interesting observations on 

 the motion of Amoeba, which has involved the discarding of 

 Prof. Ehumbler's hypothesis which was adopted in the third 

 edition ; (2) the inclusion of some new and interesting results 

 on the physiology of the bivalve Mollusca ; (3) the adoption of 

 Dr Ridewood's results on the development of centra, which have 

 narrowed the gap between the so-called arco-centra and chorda- 

 centra ; and (4) the rewriting of the section dealing with Human 

 races in accordance with the views of Ripley, Elliot-Smith, 

 Keith and other modern Anthropologists. 



A. E. S. 



E. W. M. 



I wish to state that owing to pressure of duties as Vice- 

 Chancellor, and other claims on my time, the Fourth Edition has 

 been revised and seen through the Press by Prof. MacBride, and 

 any improvements that appear in it are solely due to him. 



A. E. S. 



