viii PREFACE 



references to the literature of the subject in the body of the work. 

 Anything like consistent historical treatment would be out of place 

 in an elementary book ; and the introduction of casual references 

 to particular discoveries, while they might interest the more 

 advanced reader by giving a kind of personal colouring to the 

 subject, could hardly fail, from their necessarily limited character, to 

 be misleading to the beginner, and to increase rather than diminish 

 his difficulties. We have, therefore, postponed all reference to tin 1 

 history of the science to the concluding Section, in which the main 

 lines of progress are set forth, and have given, as an Appendix, a 

 guide to the modern literature of Zoology. The latter is intended 

 merely to indicate the next step to be taken by the student who 

 wishes to acquire something more than a mere text-book 

 knowledge. 1 



The various Sections have been written by the authors in fairly 

 equal proportions, but the work of each has been carefully read 

 and criticised by the other, and no disputed point has been allowed 

 to stand without thorough discussion. We are, therefore, jointly 

 and severally responsible for the whole work. 



A very large proportion of the figures have been specially drawn 

 and engraved for the book. Those in which no source is named 

 are from our own drawings, with the exception of Figs. 571, 572, 

 1017, 1018, 1019, 1022, 1059, 1063, and 1071, for which we are 

 indebted to Mrs. W. A. Haswell. Figs. 1002 Us, 1005 bis, are from 

 photographs kindly taken for us by Mr. A. Hamilton. Many blocks 

 have been borrowed from well-known works, to the authors and 

 publishers of which we beg to return our sincere acknowledg- 

 ments. All the new figures have been drawn by Mr. M. P. Parker. 



We have received generous assistance from Professors Arthur 

 Dendy, G. B. Howes, Baldwin Spencer, and J. T. Wilson, and from 



1 In this connection we cannot resist the pleasure of quoting two passages, 

 exactly expressing our own views, from the preface to Dr. Waller's Human 

 Physiology, which came under our notice after the above paragraph was in type : 

 " I have given a Bibliography after some hesitation, feeling that references to 

 original papers are of no use to junior students, and must be 1 too imperfect to be 

 satisfactory to more advanced students. . . . Attention has been paid to 

 recent work, but I have felt that the gradually -formed deposit of accepted know- 

 ledge must be of greater intrinsic value than the latest ' discovery ' or the newest 

 theory. An early mental diet in which these items are predominant is an 

 unwholesome diet ; their function in elementary instruction is that of 

 condiments, valuable only in conjunction with a foundation of solid food." 



