viii PREFACE TO THE FIRST EDITION 



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 the 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 bis, 1005 bis, are from 

 photographs kindly taken for us by Mr. A. Hamilton. 2 Many blocks 

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

 publishers of which we beg to return our sincere acknowledgments. 

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



We have received generous assistance from Professors Arthur 



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

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

 ]*hysiology, 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 

 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 knowledge must be of greater intrinsic value than i ho 

 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." 



' The figures referred to are numbered 018, 619, 1091. 109:2. 1093, 1096, 

 1140, 1144, 11.-)!'. 1074. and 1078 in the 3rd edition. 



