DR. W. W. ELY S NOTES ON CHAPTER II. 289 



viz., the differences observed in the skull, and in the castoreum 

 organs, it remains to inquire whether these variations are con- 

 stant and essential, and such as characterize species, or only 

 varieties. 



The fact that the beavers of the Old and the New World present 

 certain points of difference in the skull formation is not to be de- 

 nied, and the attempt has been made to eliminate those which 

 are considered unessential from those which possess an invariable 

 character in the two races, so as to establish just grounds for the 

 specific distinction. It is important to realize the tendency to 

 variation which exists in the cranial structures, and I therefore 

 quote from Brandt, from an article "TTpon the variation of par- 

 ticular bones of the Beaver Skull," op. cit. p. 6T. 



"If we have the opportunity of comparing with each other a 

 large number of skulls of one and the same species, we not unfre- 

 quently learn, on closer inspection, that no one of them agrees 

 perfectly with the others, but that all show more or less striking 

 variations. These variations are often so considerable, that if we 

 thus examined but two or three skulls, we should have no hesi- 

 tancy in deciding, according to the prevailing method of determ- 

 ining zoological species, that there was a specific difference in 

 the animals to which such skulls belonged. The examination of 

 a larger number of beaver skulls convinced me how erroneous 

 would be a conclusion drawn from the examination of a small 

 number of specimens. 



" The following remarks, therefore, have only for their object to 

 name the variations which I have seen occur in the skulls of the 

 species Castor, and to show that it is only by several, or better, 

 by many specimens of one and the same species, that we can 

 with anj- degree of certainty determine the boundaries of such 

 species." 



In the comparisons made by Brandt of European and American 

 beaver skulls, he refers to eight of the former, and five of the lat- 

 ter variety. We have, in our collection, over ninety skulls of the 

 American beaver from the region near Lake Superior, and through 

 the kindness of Prof. James Hall, of the New York State Mu- 

 seum, and Prof Spencer F. Baird, of the Smithsonian Institution, 

 I have had the opportunity to examine skulls from other American 

 localities, in all over one hundred specimens. Prof. Baird has 



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