THE BROWN OR COMMON RAT 631 



the young commence to leave the nest and eat — they are very 

 lively. At the twenty-third day their white coat begins to 

 attain the yellowish tints of the adults ; they incessantly run, 

 jump, and climb. By the twenty-sixth day, and sometimes 

 even by the twenty-first or twenty-second day, they can leave 

 their mother, but if with her they may suckle to the twenty- 

 eighth day. The young have extraordinary vitality : one — 

 only two days old — lived after forty-eight hours' exposure in 

 September to the external air on a metal plate (Lataste, 

 344 and 374). 



Rats have a considerable development of voice, frequently 

 squeaking loudly; Johnston (240) describes one as uttering 

 a thin metallic "skikking" sound when angry, or a grunting, 

 murmuring noise when amorous. 



Genus MUS. 



1758. Mus, C. Linneeus, Sysi. Nat., 10th ed., i., 59 ; genotype, by tautonymy, Mus 

 musculus (G. S. Miller, Proc. Biol. Soc, Washington, xxiii., 19th April 191 1, 59) ; 

 in part of most authors. 



1814. Musculus, Rafinesque-Schmaltz, Pricisdes DScouv. et Travaux Somiologiques, 

 13 ; a substitute for Mus. 



1837. Leggada, J. E. Gray, CharleswortKs Mag. Nat. Hist., i., 586; genus for 

 L. booduga, Gray. 



1842. MiCROMYS, Lesson, Nouveau Tableau, Mamm., 139. 



1845. Drymomys, Tschudi, Fauna Peruana, 178 ; based on D. parvulus, Tschudi = 

 Mus musculus, Linnaeus (see Thomas in Palmer, Index Gen. Mamm., 246, 1904). 



1876. Nannomys, W. Peters, Monatsber. k. preuss. Akad. Wiss., Berlin, 480 ; based 

 on N. setulosus, Peters. 



1881. ACROMYS, E. L. Trouessart, Bull. Soc. d'^tudes Sci. d' Angers, x., 133 ; a 

 synonym of Drymomys, Tschudi. 



1896. PSEUDOCONOMYS, Rhoads, Proc. Acad. Nat. Sci., Philadelphia, 531 ; sub- 

 genus based on Mus {Pseudoconomys) proconodon, Rhoads, from Western Somali- 

 land. 



1900. Dryomys, Philippi, An. Mus. Nac. de Chile, xiv., 20; a modification of 

 Drymomys, Tschudi. 



As now defined, the genus Mus is restricted to the House 

 Mice and their allies; these, according to Miller, comprise 

 about twenty-five distinct forms, of which seven are represented 

 in western Europe. 



This is a perfectly natural group enjoying a wide natural 



