viii PREFACE 



of the frog is based upon models made from my series of 

 sections, and the account of the histology of Hydra is largely 

 new, and based upon my as yet unpublished researches. I 

 have not thought it desirable to burden the elementary student 

 with a list of references to literature, and I must ask original 

 authors to pardon me for making use of their facts and 

 arguments without acknowledgment. But in every case in 

 which figures have been taken from published works full 

 acknowledgment is made. The illustrations have been drawn 

 specially for this book ; many by Mr P. J. Bayzand,the skilful 

 artist of the Linacre Department at Oxford. Others are by 

 my friend and pupil Mr E. H. Schuster of New College, Oxford, 

 and the rest have been drawn by myself. Where not other- 

 wise stated the figures are from my own sketches and 

 preparations. 



There is a considerable difference of opinion as to the 

 limits of elementary teaching in Comparative Anatomy. For 

 my own part, I consider that the more elementary the teaching 

 is in this subject the fuller it should be, and I have not 

 hesitated to enter fully into details where a detailed description 

 seemed necessary, and have discussed certain questions of 

 theoretical importance at considerable length. Students 

 seldom begin the study of Comparative Anatomy at an early 

 age, and they should never begin it until they have mastered 

 the elements of Physics and Chemistry. I have therefore 

 addressed myself, not to children, but to persons whose 

 education is well advanced, and whilst I have tried to write 

 simply and intelligibly, I have not attempted to evade the 

 difficulties of technical language. All technical terms, where 

 used for the first time, are printed in thick type, and are 

 sufficiently explained in the context. 



Whilst the faults of this book are entirely my own, I must 

 attribute any merit it may possess to the influence of the 

 three successive occupants of the Linacre chair of Comparative 

 Anatomy at Oxford under whom I have had the honour to 

 serve, the late Professor H. N. Moseley, Professor E. Ray 

 Lankester, and Professor W. F. R. Weldon. Nor must I 

 forget the many lessons I have learned from my whilom 

 colleagues at Oxford, Professor W. Blaxland Benham and 

 Professor E. A. Minchin, 



