106 Records of the Indian Museum. [Vorseve 
that these varieties appeared in the first case as the offspring of 
normal self-coloured parents ; even if, as I believe, we are justified 
in making the assumption, there is no evidence to show whether 
the normal parents produced successive and entire litters of ab- 
normal offspring, or an occasional ‘‘ black sheep’’ from time 
to time. Judging from events which have been recorded from time 
to time it seems that the latter is the more likely supposition. 
The following statement will illustrate the way in which the 
question often presented itself: While in Madras City I had, 
during three days, the opportunity of seeing more than a thousand 
common house rats, and as a result of a somewhat cursory examina- 
tion, I concluded that all were of the common brown whole- 
coloured type of Mus rattus ; but from among them I picked out two 
which had a pure white line in the middle of the breast. The con- 
clusion that one naturally jumps to is that these two, or their parents, 
or a near ancestor which showed the same peculiarity, must have 
been the offspring of normal parents. Although this conclusion is 
not supported by any actual evidence, it appears to be sound because 
we cannot find any other explanation. 
But even if we regard their primary origin as uncertain, there 
is no shadow of doubt but that these abnormal rats sometimes occur 
in groups which may occupy two or more adjacent houses from 
which the normal rats have been displaced. It is this particular 
point which I wish to emphasize. The question was first placed 
beyond doubt in the case of the black variety of Gunomys bengalensis 
which was found in Rangoon. Twelve rats of this kind were caught 
in two adjacent houses, and no other rats of any kind entered the 
traps set in those houses during the time of their capture. It is 
certain that the black variety of G. bengalensis is not a common 
rat in Rangoon, and it has never been found except in Rangoon. 
During the year of my visit there, rats were being caught at the 
rate of four thousand a day. Before these twelve peculiar rats 
were captured, others like them had been brought very occasionally 
to the collecting stations, but it was not until nearly six months 
after the capture of the twelve, that two others were obtained. 
There is apparently no reason why these black rats should not have 
increased in numbers until they occupied ten or a hundred houses. 
Their success or failure would of course be decided in the stress 
of that competition which occurs among all living things. 
Finally, there is a probability that established races such 
as are recognised by taxonomists as ‘‘ good species ’’ have arisen 
in the way indicated: because the characters upon which these 
species have been defined, are in some cases exactly the same as 
those which are found in the abnormal individuals or sports which 
occur along with the normal rats of India. For example, the 
character of albiventralism is a peculiarity of many well-known 
species of the Mus vattus group. A more striking example is pre- 
sented by those species of rats in which the terminal third of the 
tail is white. The species Mus blanfordi, which is found in the hills 
of Madras, possesses this character, as do other species which have 
