

TREF ACE 



While most readers seeking comprehensive information may have had their attention 

 cbawn to the generalizations contained in the first part of this work, the naturalists who 

 have studied the second and third parts may have noticed that the subjects imder consider- 

 ation there are treated in a different manner from that generally adopted in similar investi- 

 gations. Confident that what have been called our classifications are in reality the various 

 readings of a system which truly exists in nature, I have endeavored to show, that, in 

 arranging their systems, zoologists have unconsciously followed great natural relations in the 

 animal kingdom, and that what they have supposed to be their invention was only their 

 instinctive perception of an order which unites under a consistent plan all the isolated facts 

 studied by them. My first step in the attempt to demonstrate this proposition was to collect 

 all the facts relating to our science and to compare them carefully with the systems, testing 

 the one by the other. By the coincidence of the two I hope to have proved tliat the Power 

 which originated the facts must also have originated the ideas expressed in the systems ; and 

 that the latter are true only so far as they adhere to tlie great system of Nature from which 

 they have been transcribed. The first monograph, limited to a single Order, afforded, how- 

 ever, a meagre field for such a demonstration; though it was broad enough to allow of 

 the attempt without modifying too much the usual mode of treatment of such subjects. 

 But finding, after many years' application of that method in my own investigations, that, 

 far from complicating my studies, I only derived daily additional facilities in tracing the 

 manifold relations which unite all kinds of natural groups among animals, I have resolved 

 upon combining, through the presentation of a whole Class, the description of the facts, with 

 a critical analysis of their meaning, as far as they have a bearing upon classification. How 

 successful the attempt has been, time will show. 



In selecting the class of Acalcphs for such an experiment on a larger scale, I was influ- 

 enced by the circumstance that these animals had attracted my special attention for many 

 years past; and that, being particularly familiar with them, it was easy for me to treat 



