Volume V. June, i8gi. Ntimber i. 



JOURNAL 



MORPHOLOGY. 



ON THE OSTEOLOGY OF PCEBROTHERIUM : A 

 CONTRIBUTION TO THE PHYLOGENY OF THE 

 TYLOPODA. 



W. B. SCOTT, 



College of New Jersey, Princeton. 



Although the theory of evolution is now accepted as an 

 established fact by almost all naturalists, this general agree- 

 ment does not extend beyond the point of believing that the 

 present organic world has arisen by descent from simpler forms. 

 The application of the theory to concrete cases is beset with 

 grave difficulties, and gives rise to the most divergent views. 

 The uninitiated reader who takes up a monograph upon some 

 animal group may well be surprised to see the minuteness and 

 accuracy with which the genealogy of the series is set forth, 

 and the relationships of the various genera and species mar- 

 shalled in orderly array. But another treatise upon the same 

 animals will contain an equally complete family tree, which 

 contradicts the first in almost every particular. To some extent 

 this almost hopeless divergence is inherent in the very nature 

 of the problem, it being largely a question of the value of evi- 

 dence and of the balance of probabilities, as to which men must 

 be expected to differ ; but there is another potent cause of the 

 discrepancy. When the contradictory phylogenetic schemes are 

 analyzed, it is frequently found to be the case that the discus- 

 sion rests upon certain postulates and assumptions, sometimes 

 explicit, generally only implied, and even apparently uncon- 



