178 Reviews. [Jan. 
even slight differences of colour and size, if found to be constant, are suf- 
ficient to constitute such individuals a distinct race or species. When such 
differences are found to co-exist with a different geographical distribution, 
I certainly prefer the views of those who look on all permanent distinctions 
of colour, size, structure, &c., as distinct species; and I believe that no change 
of climate, or food, or other external circumstances, will produce any altera- 
tion in them or in their descendants, if they remain true to each other ; 
and as yet I know of no recorded instance where any well-marked race has 
produced offspring differing from their own, or tending to revert to a 
supposed original type. That various nearly-affined species will propagate 
inter se, and produce fertile offspring, I fully believe; as in the cases of 
the green Pigeons of Bengal and of Southern India, in the Indian and the 
Burmese Rollers, the small Cuckoos of South India and those of Bengal, 
and in several other instances: but that this fact militates against their 
being species and in favour of their being varieties, I think is not sup- 
ported by many recent experiments in crossing. Of late years many 
species have been universally admitted as such, which were formerly con- 
sidered simple varieties, and although, perhaps, the tendency of late 
writers has been to multiply species, in some cases most unnecessarily, 
yet in previous years the other extreme was taken, more especially by 
Schlegel and his followers. Our best naturalists and ornithologists now 
fully recognize the distinctness of permanent races. If varieties are once 
allowed, it depends on individual judgment or caprice to what extent they 
may be carried. In this country, where there are many very closely allied 
Species, among genera characteristic of the country, many of the species 
of Malacocercus and Hematornis would be classed as simple varieties by 
some, whilst others would perhaps allow some of them, whose different 
notes they might have observed, to be distinct species, and the rest 
varieties. Lastly: it is, I think, more convenient in practice to give each 
race a distinct specific name, than to speak of them as ‘ Var, A,’ or 
‘Var. BY’ of such a species.” 
With revard to the origin of these allied or “representative ” 
species, as they are usually termed, Dr. Jerdon states that, as far as 
his “brief experience goes, geographic distribution is against Mr. 
Darwin’s theory. ‘‘'To give one instance,” he continues, “ Malaco- 
cercus striatus of Ceylon is more allied to M. Bengalensis of Bengal, 
than to M. Malabaricus, which is spread throughout a vast region 
between those provinces.’ On this point we may remark that the 
great mass of evidence in such cases is, as is now generally allowed, 
decidedly on the other side of the question. It is beyond a doubt, 
that allied species, are as a rule, distributed geographically in the 
order of their affinities, that is, that the most nearly allied occupy con- 
terminous areas. Moreover, Dr. Jerdon ought to be aware that 
Ceylon, though now-a-days much more nearly connected with the 
peninsula of India, than with the upper provinces, furnishes many 
remarkable forms which tend to show that this island has been peopled 
with life from the other side of the Bay of Bengal, along which the 
Bengalese species descend, often far to the south. Dr. Jerdon, how- 
ever, seems to take a very candid view of Mr. Darwin’s theory on 
other points, though he is of opinion that that distinguished naturalist, 
“perhaps, lays too much stress on external and fortuitous cireum- 
stances as producing varieties, and not enough on the inherent power 
of change.” 
