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 &. xorvegicus. 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 zorvegicus. Blind rats (four out of a litter of five) 
have been recorded by Cocks (Zoologist, 1903, 430), who informs us 
(cz lit.) of two other cases from Poynetts, near Henley, viz., three out 
of five young rats (head and body, 100 to 110 mm.) on 8th January 
1904, and another about two-thirds grown on 16th July 1914. The 
cause of the blindness appears to be obscure though post-natal (see 
below, p. 641). 
Geographical variation :—The only race at present recognised as a 
distinct sub-species from the typical European Brown Rat is &. x. 
primarius, Kastchenko, described from the Trans-Baikal region. 
This form is represented in the British Museum collection by a 
series collected in July 1914 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. 
1R. I. Pocock, Fzeld, 15th June 1907, 1015; and zézd., 18th 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 F%e/d, 27th June 1908, 1117). 
» D. E. Lantz, The Brown Rat in the United States, 1908, 14. 
3 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. 2k 
