BIOLOGICAL .NOTES UPON FIBER, GEOMYS AND 



ERETHYZON. 



By C. L. and C. Judson Herrick. 



It has been considered appropriate to prefix to the account by one 

 of us of certain neurological peculiarities of the above mentioned ro- 

 dents, a brief statement respecting their habits and some points in 

 their anatomy more or less directly bearing upon their nervous struc- 

 tures. The three groups are widely separated, and yet have a number 

 of curious similarities, or rather agree in certain differences from other 

 rodents in a way which may serve to justify the comparison as well 

 as the contrasting of the types selected. 



The Muskrat, Fiber zibethicas, is sufficiently well-known to 

 every one, and yet perhaps few are aware of the extent to which the 

 animal adapts itself to the varying conditions of its environment. 

 One who casually learned to know the water rat in one of our western 

 states might pass many years in Ohio without recognizing the fact that 

 the same animal abounds in Ohio, and under the changed conditions 

 here prevailing adopts an almost wholly different method of life. It 

 would be more accurate to say that in the cold North-west, with its 

 luxus of small lakes and marshes, the monotonous career of the ani- 

 mal expands in conformity with the greater variety of aquatic stations. 



The muskrat is a truly Arvicoline rodent, that is, its affinities are 

 with the field mice rather than with the jumping mice (Hesperomys) or 

 oriental rats and mice (Mus). Though, at first sight, very different 

 from Arvicola, the chief differences in Fiber are such as are obviously 

 adapted to aquatic habit. The long, laterally flattened, scaly and 

 naked tail, small ears, obliquely set and fringed hind feet with 

 webbed toes are all modifications induced by accommodation to 

 acquatic habit. The dark brown fur is long, with a liberal admixture 

 of long, stiff, glossy hairs of a darker color than the rest. The color 

 and texture varies with the season and in early summer rats may be 

 found with a curiously tufted or mottled pelage. There are six 

 mammae and strongly developed perineal glands which are responsible 

 for the peculiar musky odor implied by the name. The secretion is 



