PREFACE. 5 



The dissection of a single representative of each of the 

 principal divisions of the Invertebrata will give the student 

 a more real acquaintance with their comparative anatomy 

 than any amount of reading of this, or any other book. 

 And I have endeavored to facilitate practical study by 

 supplying a somewhat full description of individual forms, 

 in the case of the more complicated types. 



That the power of repeating a " Classification of Ani- 

 mals," with all the appropriate definitions, has anything 

 to do with genuine knowledge is one of the commonest 

 and most mischievous delusions of both students and their 

 examiners. 



The real business of the learner is to gain a true and 

 vivid conception of the characteristics of what may be 

 termed the natural orders of animals. The mode of ar- 

 rangement, or classification, of these into larger groups is 

 a matter of altogether secondary importance. As such, I 

 have relegated this subject to a subordinate place in the 

 last chapter ; and I have thought it unnecessary, either to 

 discuss the systems proposed by others, or to give reasons 

 for passing over, in silence, my own former attempts in 

 this direction. 



Of the manifold imperfections in the execution of the 

 task which I have set myself, few will be more sensible 

 than I am ; but I trust that the book, such as it is, may 

 be of use to the beginner. 



Those who desire to pursue the study of the Inverte- 

 hrata further will do well to consult the excellent treatises 

 of Yon Siebold, 1 Gegenbaur, 3 and Clans ; 3 and the elabo- 



1 " Lehrbuch der vergleichenclen Anatomie der wirbellosen Thiere," 1848. 

 One of the best books on the subject ever written, and still indispensable. 



2 " Grundziige der vergleichenden Anatomie," 1870 ; and " Grundriss der 

 vergleichenden Anatomie," 1874. 



3 " Grundziige der Zoologie." 3tte Auflage, 1876. 



