INTRODUCTION. 5 



has already pointed out in the case of the arbitrary clas- 

 sifications of the Lepidoptera. When all this knowledge 

 is brought together, assorted, and systematically used, 

 then the sequence of life upon our planet will be demon- 

 strated as never before. Then the isolation method of 

 arrangement to which I have alluded will be relegated 

 to the past and students will no longer receive the lasting 

 impression that fossil forms are distinct creations having 

 no connection with living organisms, but each museum 

 will be in itself a revelation of the essential unity of all 

 animal life. 



It is true that many of our museums are so con- 

 structed that they are ill adapted for the demonstration 

 of the evolution of inorganic and organic nature. But 

 where this demonstration cannot be given with complete- 

 ness, minor collections like a Synoptic Collection of geo- 

 logical or zoological specimens may point out the way to 

 the desired end. 



The following principles of classification Professor 

 Alpheus Hyatt wished to have carried out in the Synop- 

 tic Collection of this Museum, of which he was Curator 

 during the preparation of nearly all of this Guide. 



First : In the arrangement of the material proceed 

 always from the simple to the complex. 



Second : So far as possible let each group be repre- 

 sented first by its primitive ancestors that lived in the 

 pre-Cambrian, Cambrian, or early Palaeozoic times. 



Third : From these primitive ancestors pass to the 

 embryonic and larval stages of generalized members of 

 the group existing to-day ; and from these early stages to 

 the adult stages which are invariably more specialized. 



Fourth : From the generalized adult members in every 

 group proceed to the specialized members which have 

 reached their present condition through the law of spe- 

 cialization by addition. 



Fifth : In some of the most impressive instances go still 

 farther to those extremely specialized adults which have 

 become so by the law of specialization by reduction. 



