300 APPENDICES. 



the spread of a single species over botli continents. That long 

 separation should have developed certain peculiarities of structure 

 might reasonably be expected. From the observed tendency to 

 variation exhibited by the skulls of consanguinei, we should 

 even expect to find these differences greater, in separated races, 

 than actually occurs. There appears, therefore, to the writer, to 

 be no necessity for assigning a separate and distinct origin to the 

 beavers of the Old and the New World, in order to account for 

 the differences which have thus far been observed between them. 



III. Castoreum Organs, and Generative Organs, 



The beaver has long been celebrated for the peculiar secretion 

 called castoreum, which has been much used in medicine. Other 

 animals furnish highly odorous secretions, of which musk and 

 civet are examples, the uses of which in relation to the animals are 

 not well understood. Although much attention has been paid to 

 the anatomy of the beaver, the organs furnishing the castoreum 

 have not un frequently been erroneously described. It will be 

 seen in the descriptions and figures which follow, that the beaver 

 has two sets of glandular organs, lying below the pubis, of which 

 the upper pair furnish the castoreum, and the lower, an oily secre- 

 tion. In the Le9ons d'Anatomie Comparee (Cuvier), vol viii. 

 p. 245, also in the Dictionnaire des Sciences Medicales, Art. 

 Castor, and in the U. S. Dispensatory, by Wood & Bache, the 

 castoreum is incorrectly referred to the lower pair of organs, and, 

 again, both the upper and lower glands have been said to furnish 

 this secretion. 



The beaver has but a single orifice for the genito-urinary and 

 the intestinal organs, and there is nothing in its external appear- 

 ance by which its sex can be determined. 



When the animal is laid on its back there is a space between 

 the pubis and the scaly tail about seven inches long, covered with 

 hair like the rest of the body. In the centre of tliis space is the 

 upper margin of the cloacal orifice, which is one and a half inches 

 in length, just within which, at the lower margin, is the orifice of 

 the intestine. The width of the tail where the scales commence 

 is about four inches. 



On dissecting off the skin, the skin muscle is brought into view, 



