METHODS OF PALAEONTOLOGICAL INQUIRY. 77 



method has long been followed, and with brilliant results, in the 

 case of the Ammonites, but only of late has material been 

 collected in sufficient quantities to make it applicable to 

 mammals. 



With all its difficulties and drawbacks, palaeontology pos- 

 sesses certain preeminent advantages over other methods of 

 morphological inquiry. The observer deals, not merely with 

 contemporary forms, whose likenesses or unlikenesses to one 

 another must be arbitrarily valued, nor with embryonic stages 

 whose characters must be interpreted according to the judg- 

 ment of the individual worker, but with the actual line of 

 descent and in its true order of chronological succession. This 

 is an advantage the importance of which can hardly be over- 

 estimated, and one which justifies the expenditure of unlimited 

 time, labor, and money in the work. This it is, more than any- 

 thing else, which encourages the worker to persevere in spite 

 of every obstacle, content if years of labor result in the full 

 knowledge of a few forms and the identification of a few links 

 in a phyletic chain. 



In the investigations which we have so far considered the 

 whole stress has been laid upon morphology, and for their suc- 

 cessful prosecution great numbers of finely preserved specimens 

 are required ; but there are other lines of inquiry in which very 

 shabby and fragmentary fossils may be of great service. One 

 of these subjects is the fascinating one of the geographical dis- 

 tribution of mammals. It is already possible to analyze the 

 existing North American fauna and point out the indigenous 

 elements derived from a long line of native ancestry, and to 

 identify the immigrants from the Old World and from South 

 America. In many cases we may go so far as to specify the 

 geological date of the migration. Further, we can, in several 

 instances, prove the American origin of certain faunal elements 

 now confined to other continents. For this purpose complete 

 specimens, though desirable, are not indispensable. Genera 

 and species may usually be identified from the teeth alone, 

 and, while phylogenies cannot be safely constructed from 

 such material, the cardinal facts of distribution may be thus 

 determined. 



