PREFACE 



FOR about a quarter of a century this book now revised 

 -has had an apparently useful life as an introduction to 

 zoological science. Its plan is simple : 



(a) It begins with the everyday life of animals, their 

 haunts, their inter-relations, their struggles, their in- 

 dustries, their family life, their behaviour, and their 

 internal activities. 



(b) The second aspect considered is that of structure 

 the multitudinous forms of animal life and their archi- 

 tecture. 



(c) The third part has to do with the continuance of 

 the race and with life-histories. 



(d) Finally, the facts and problems of evolution are 

 illustrated. 



The four parts of the book correspond broadly to 

 Physiology, Morphology, Embryology, and Etiology, but 

 there has been no punctilious observation of boundary- 

 lines. 



The four parts of the book will appeal to students of 

 different tastes. For some are most interested in habits 

 and functions, others in form and structure, others in 

 development and life-history, and others in the general 

 problems of evolution. Each of these aspects has its 

 own interest, and the student should begin with the one 

 which most attracts him. But all must be taken into 

 account if we are to get an all-round view of animal life. 



f >X J- A. T. 



UNIVERSITY OF ABERDEEN, /^ 

 1916. / ( 



