mi COMPARATIVE ANATOMY AND PHYSIOLOGY. 



referring to, sometimes perhaps insisting on, the dif- 

 ferent methods by which similar results are attained by 

 different animals. That which I have most constantly 

 kept before myself, and which I hope the student 

 will faithfully bear in mind, is, that there has been an 

 evolution of organs as well as of animals, and that he 

 who desires to understand the most complicated organs 

 must first know the structure of such as are more 

 simply constituted. 



In pursuit of this object, I have written about 

 organs rather than about groups of animals ; but I 

 have added an index in which the various parts of 

 an animal are collected under the head of its name ; 

 so that the student who desires to use this manual as 

 a zoological text-book will have no difficulty in 

 selecting the portions of the chapters which bear on a 

 particular form or set of forms. 



I have departed a little from the ordinary method 

 of writing a handbook, in somewhat plentifully inter- 

 spersing the names of my authorities for various 

 statements. I have done this, not only because it 

 recommends itself to my sense of justice, but because 

 zoological science is just now advancing so rapidly 

 that many observations and suggestions have to be 

 incorporated, even in a text-book, before they become 

 the general property of zoological workers. My 

 indebtedness to the personal teaching and the pub- 

 lished writings of Professor Ray Lankester must be 



