PREFACE 



In the following pages I have endeavoured so to treat of 

 the animals which are most often studied in courses of 

 Elementary Zoology as to introduce the student by their 

 means to the principal problems of the science. J have 

 tried at the same time not to state facts in terms of any 

 theory, but to expound theories after the facts upon which 

 they are based. I have assumed that the student will have 

 an elementary knowledge of Chemistry and Physics. 



One general principle has guided me — that the organism 

 should be regarded as a whole. Thus I have not adopted 

 views which ascribe to certain morphological constituents 

 of the body of an organism, such as cells and zooids, a 

 mystical "individuality," based upon assumptions with 

 regard to their history or potential independence. I have 

 taken indivision, not indivisibility, to be the essence of 

 individuality. 



My very sincere thanks are due to a number of gentle- 

 men for assistance of various kinds. Professor J. Stanley 

 Gardiner has been kind enough to read almost the whole 

 of the work, and has given me invaluable advice. Mr. 

 J. Barcroft, Mr. H. H. Brindley, Mr. C. Clifford Dobell, 

 Mr. L. Doncaster, Dr. H. Gadow, Professor E. W. 

 MacBride, and Professor R. C. Punnett have each seen 

 portions of the book, and I am greatly indebted to each 



