PREFACE vii 



given in my brother's published works ; and, in Part II, .1 

 have intentionally made use of these descriptions, borrowing 

 very freely from the Elementary Biology, as well as (with 

 Professor Has well's permission) from the Textbook of 

 Zoology ; and to a less extent, from the Zootoiny. 



The practical directions are mainly based on a series of 

 Laboratory-instructions I drew up some years ago for the 

 use of my junior classes, which consist principally of 

 students preparing for the Intermediate Science examin- 

 ation of the University of Wales, the Preliminary Scientific 

 examination of the London University, and the first ex- 

 amination of the Conjoint Board of the Royal Colleges of 

 Surgeons and Physicians. The time such students can 

 devote to an elementary course in the subject is limited ; 

 and throughout the book I have borne in mind that the 

 main object of teaching Zoology "as a part of a liberal 

 education is to familiarise the student not so much with the 

 facts as with the ideas of the science," but at the same 

 time that he should be provided with a sound basis of facts 

 so arranged, selected, and compared as to carry out this 

 principle. 



Our original intention was to include one or more examples 

 of each of the larger phyla, and also to add a practical 

 exercise after each type, giving general directions for the 

 examination of an allied form for comparison. But I 

 found that this would be impossible within the space of a 

 single volume, and it was therefore necessary to limit the 

 descriptions mainly to those animals to which the students 

 for whom the book is chiefly intended have to give special 

 attention. This has resulted in rather a heavy balance on 

 the side of Vertebrates ; but on the whole, I think that if 

 sufficient work is done on the lower animals to illustrate 

 certain main facts and generalisations, a comparative study 



