38 CASTOROLOGIA. 



sive definition, and understand the word species to include " all 

 living forms which have the most essential properties in common, 

 are descended from one another and produce fruitful descendants ;" 

 though all the facts of natural life cannot be arranged agreeably to 

 this conception, and a compromise has often to be effected by the 

 creation of a sub-species as a grade between species and variety, where 

 difiiculties arise in attempting to draw a sharp line; for varieties 

 which have arisen from one species may differ more from one another 

 than do distinct natural species ; thus the absence of a positive test, 

 leaves the matter to the individual judgment of the observer to decide 

 between species, sub-species and varieties. The higher groups of 

 systematic zoology are of course freer from these confusions, thus 

 the "order" comprises all the genera which conform to a simple 

 character, (as for instance, that set forth at the beginning of this 

 chapter), and the " genus " is an assemblage of species having fur- 

 ther points of structure in common. Carl lyinnseus (i 707-1778,) was 

 the greatest systematizer of zoology, and to him also we are indebted 

 for the present form of nomenclature, by which every animal receives 

 two names taken from the Latin language, the generic name, which 

 is placed first, and the specific name, which together indicate that the 

 character of the animal has been sufficiently defined to place it in a 

 scientific arrangement with the whole system of life. 



With this digression, we have become ready to appreciate the 

 value of the following varieties of the Canadian beaver. They are 

 best recorded in Dr. John Richardson's " Fauna Boreali Americana" 

 where they are treated in the inverse order of rarity. The first 

 variety, "nigra" — the black beaver, and although these are not 

 accounted rare, they are only found in the proportion of one to ten 

 thousand of the normal color. It should here be remarked that the 

 natural color is very variable and is most correctly described as of a 

 chestnut brown, ranging towards the south to a pale yellowish brown, 

 and in the north approaching a blackish brown. The black beaver, 

 however, has more than a mere relative coloring and is unquestion- 

 ably an evidence of melanism — an excessive development of pigment 

 in the skin and its appendages. Hearne recognised the beautiful 

 gloss of the fur, and the shading must be described as bluish rather 



