1 1 
with reference to the Dying Out of Species. 
Now whatever cause makes all these species of this graduated degree 
of rarity must be a cause which acts equally upon all. Family by family, 
and genus by genus, all alike obey the same law, and have some species 
VR, or confined to a very minute area ; some R, or confined to an area of 
about twelve to twenty-four miles in diameter, and rare in that ; some RR, or 
occupying an area of forty to fifty miles in diameter ; some RC, with yet larger 
territory, and commoner in that, and so on. The Ceylon-Peninsular-Indian 
species, and the widely distributed forms, show exactly the same phenomena, 
but, as would be expected upon my hypothesis, show greater trial and error 
variation among themselves. The order of appearance of new species in 
Ceylon is more likely to be regular than the order of appearance in the 
island of species from abroad, and new species, confined to small areas, 
are perhaps more likely to show adherence to the law in detail than more 
widely distributed species, which may enter the island, for anything we can 
tell, at several points more or less simultaneously. 
It is inconceivable that Natural Selection, which is an agent of essen- 
tially differentiating nature, should thus act with uniform pressure upon 
every family in the flora, and upon every larger, one might say every, 
genus. The only cause that I can conceive that thus acts is age. Young 
endemic species, and newly arrived species from abroad, show rarity VR, 
but as time goes on they will creep slowly up to R, and later to even higher 
stages in degree of commonness. Working upon averages of, say, twenty 
they all behave alike, but in any individual case of course the rate of 
progress will be determined by degree of local adaptation, and still more 
by chance, so that of two species starting on the same day at the same 
degree of rarity VR, after a certain lapse of time the one may have reached 
RC, the other only R. 
To me this arithmetical argument appears to clinch the matter, 1 but 
as it may not appeal to those who have not an arithmetical turn of mind, 
it will be well to put what is much the same argument into a biological 
dress. Taking from Trimen’s Flora of Ceylon the first few endemic species 
of the degree of rarity VR, R, and RR, and marking their position (if VR) 
or drawing a ring round their recorded localities (if R or RR), we get the 
results shown in the three little maps (Fig. i). The localities are not shown 
with absolute accuracy in these little maps, but nearly enough for the 
purpose. I have much pleasure in acknowledging the help I have received 
in identifying the localities from Mr. Frederick Lewis, late of the Land 
Settlement Department in Ceylon. 
Comparing these three maps, the first thing to be noticed is that each 
is like the others, but with different sizes of area. The VR species cover 
the map (if the whole 233 were taken) with a pattern of small dots or lines. 
1 So far as Natural Selection is concerned. 
