THE BROWN OR COMMON RAT 617 



and others, from a Mendelian standpoint. Pocock^ states that all 

 the fancy rats kept or seen by him were unmistakably speci- 

 mens of norvegicus ; and Lantz^ says that the only albino rats in 

 the collections of the United States National Museum and Biological 

 Survey are of this species. It is therefore very doubtful, despite 

 statements to the contrary,^ whether any of the tame rats of commerce 

 are other than E. norvegicus. Lataste (314) thinks that the white 

 variety is the commonest and most ancient of these tame races — 

 it being known to his friends from at least about 1857 — and that 

 the other varieties are rarer and more recent productions. Millais 

 (ii., 218) says that although there was a National Mouse Club in the 

 nineteenth century, it was not until the twentieth century that classes 

 for fancy rats came into notice at the shows. 



Brehm {Thierleben, ii., 125) mentions artificial "King Rats" (see 

 p. 592) as known in 1774 and 1822, and Lataste (352) thinks they must 

 have been tame norvegicus. Blind rats (four out of a litter of five) 

 have been recorded by Cocks {^Zoologist, 1903, 430), who informs us 

 [in lit.) of two other cases from Poynetts, near Henley, viz., three out 

 of five young rats (head and body, 100 to 1 10 mm.) on 8th January 

 1904, and another about two-thirds grown on i6th July 1914. The 

 cause of the blindness appears to be obscure though post-natal (see 

 below, p. 641). 



Oeographical variation : — The only race at present recognised as a 

 distinct sub-species from the typical European Brown Rat is E. n. 

 primarius, Kastchenko, described from the Trans-Baikal region. 

 This form is represented in the British Museum collection by a 

 series collected in July 19 14 by Mr G. A. Burney at Musavaia, 

 Trans-Baikal, and Leestvineechnova, Irkutsk. It is characterised 

 by its somewhat shorter tail (averaging about 76 per cent, instead 

 of about 82 per cent, of the length of the head and body) ; smaller 

 hind feet (31 to 37-5 mm.); longer and softer fur, and darker dorsal 

 coloration. The tail is rather densely clothed with very fine silvery 

 hairs; its skin is distinctly bicoloured in younger specimens, but 

 apparently has a tendency to become paler above with advancing age. 

 The feet are silvery white. The young have a very soft and full 

 coat, dusky above, leaden below; a few of the hairs on the head 

 and shoulders have yellowish-brown tips, while those of the under parts 

 are silver-tipped. 



' R. I. Pocock, Field, 15th June 1907, 1015 ; and ibid., i8th May 1912, 997. 

 Capt. S. Flower mentions, in the Report of the Giza Zoological Gardens, the births 

 of many white rats of this species in 1907 (see also Field, 27th June 1908, 11 17). 



''■ D. E. Lantz, The Brown Rat in the United States, 1908, 14. 



' Cf, Millais (ii., 217) : " It is scarcely necessary to say that all the rats sold in 

 the fanciers' shops are domesticated varieties of Mus rattus." 



VOL. II. 2 R 



