284 Mammals of Eastern Asia 
tions of the British Museum included 38 species groups and 554 
forms. The headquarters of the genus is tropical southeastern 
Asia, where no less than thirteen major species groups are 
found. These become fewer as one moves away from the center : 
nine in Burma, six in south China, three in India, three in 
north China, two in Europe. In Africa, a second center of 
speciation, nine groups are present. Two of the groups, the 
semi-domestic Norway Rats and the Alexandrine Rats, are com- 
mon to all the regions named and have been accidentally carried 
on ships to North and South America and most of the islands of 
the oceans. 
The Rats are strongly variable in size and in the color and 
quality of the fur, as one species or another is examined. The 
number of nipples varies in different species from 4 to 12. But 
all look "rat-like," with substantially similar body form, and 
the tails, apparently bare and scaly, longer or shorter than the 
head and body, according to species. 
Some of the species groups comprise very few species ; others 
include many forms of Rats. Some have restricted geographical 
ranges; others are represented over enormous territories. In a 
general way, the Rats of a given group conform to rather a 
narrow range of size. Six of the groups that show markedly 
local distribution are : Rattus canus, cremoriv enter, whiteheadi, 
eha, bowersi, and berdmorei. Four more, having broader geo- 
graphical patterns, reaching especially into the Sunda Islands or 
into southern China, are R. miilleri, confucianus-huang, rajah, 
edwardsi-sabanus. One, R. concolor, the smallest and most 
mouse-like of Rattus groups, has extended itself to New Guinea 
and most of the islands of the Pacific Ocean. Two, R. rattus 
and norvegicus, include the parasitic Rats that, as previously 
mentioned, have been distributed by man all over the world. 
A synopsis of the present arrangement of the oriental Rats 
of the genus Rattus: 
