RECENT LITERATURE 
147 
is a motley horde, representing the progeny of truly native rats crossed with the 
descendants of old wanderers and with newcomers not only from the neighbouring 
hinterland but from all parts of the world. It is therefore only in the more 
remote parts of the country that we can reasonably expect some measure of 
success to crown such efforts 
Mr. Wroughton has already brought before the Society (J. B. N. H. S., Vol. 
XXIII, p. 474) the view that the white bellied forms of R. rattus in India and 
Burma represent the primitive wild form of the species ; and that the dark bellied 
types are parasites, the darkening of the underparts, no less than the darkening 
of the back, being the outward indication of domesticity or parasitism. In 
support of this view, one may point to the general similarity of the Indian white 
bellied forms to the wild race, R. r. frugivorus, of the Mediterranean region; to 
their wide distribution, both in the mountains and in the plains, in India and 
Burma: and to the wild life which many of them lead in the jungles. Further 
on investigating these white bellied rats in detail, we find that they behave very 
much as do normal wild mammals as regards geographical variation and that 
it is therefore possible and comparatively easy to arrange them in geographical 
races or subspecies. 
With regard to the dark bellied rats the case is different. They are largely 
restricted to districts possessing substantial houses; they are more frequently 
caught within doors and far less frequently in the open. Close investigation of 
their structure leads to nothing but confusion ; the variation is largely individual 
or colonial, and scarcely at all geographical. In some districts, as in Kumaon, 
such rats seem to have little or no connection with the white bellied forms; in 
other places, they differ from their white bellied companions merely in colour 
and to a trifling extent in skull — the cranial differences being readily susceptible 
of a physiological explanation, . . . .; finally, in still other districts, the 
difference is purely one of colour and even that sometimes breaks down. One 
concludes from this that the dark bellied rats are of diverse origin; some seem 
to have been produced, in the localities where they are now found, from the local 
white bellied race; others have found their way to their present habitations 
from other more or less remote districts of the country, or even from abroad; 
and lastly, many are doubtless to be regarded as the mixed descendants of both 
native and imported stocks.” 
It will readily be seen that the interrelationships of these rats presents a com- 
plicated problem and one which is rarely met with among mammals. Of particu- 
lar importance is Mr. Hinton’s suggestion that, in the Rattus rattus group, dis- 
tinct subspecies are probably being developed in different ‘‘niches in nature” 
at single localities. While the facts now at hand may not be sufficient to prove 
the occurrence of such development among the rats under discussion they clearly 
indicate the possibility that it is taking place. Something of the kind must be 
assumed as the first step in establishing lines of “local adaptive radiation,” a 
process which appears to have exercised great if not dominating influence through- 
out the evolutionary history of all mammals. At present, however, this process 
is known from its later or finished results only; its earlier stages have not been 
demonstrated. Detailed observations on the living house rats of India in their 
natural surroundings are therefore much to be desired. A clear understanding 
of the early stages of adaptive radiation might be one of the results. 
—G. S. Miller. 
