12 MR. A. R. WALLACE ON THE PAPILIONIDÆ 
all seem equally constant; and as most of these had already been named and described 
as species, I have added the New Guinea form under the name of P. Penelope. We thus 
get a little group of Ulyssine Papilios, the whole comprised within a very limited area, each 
one confined to a separate portion of that area, and, though differing in various amounts, 
each apparently constant. Few naturalists will doubt that all these may and probably 
have been derived from a common stock; and therefore it seems desirable that there 
should be a unity in our method of treating them : either call them all varieties or all 
species. Varieties, however, continually get overlooked ; in lists of species they are often 
altogether unrecorded ; and thus we are in danger of neglecting the interesting phenomena 
of variation and distribution which they present. I think it advisable, therefore, to name 
all such forms; and those who will not accept them as species may consider them as sub- 
species or races. 5 
6. Species —Species are merely those strongly marked races or local forms which, when 
in contact, do not intermix, and when inhabiting distinct areas are generally believed to 
have had a separate origin, and to be incapable of produeing a fertile hybrid offspring. 
But as the test of hybridity cannot be applied in one case in ten thousand, and even if it 
could be applied, would prove nothing, since it is founded on an assumption of the very 
question to be decided—and as the test of separate origin is in every case inapplicable— 
and as, further, the test of non-intermixture is useless, except in those rare cases where 
the most closely allied species are found inhabiting the same area, it will be evident 
that we have no means whatever of distinguishing so-called “true species " from the 
several modes of variation here pointed out, and into which they so often pass by an 
insensible gradation. It is quite true that, in the great majority of cases, what we term 
“species ” are so well marked and definite that there is no difference.of opinion about 
them 2 but as the test of a true theory is, that it accounts for, or at the very least is not 
inconsistent with, the whole of the phenomena and apparent anomalies of the problem ` 
to be solved, it is reasonable to ask that those who deny the origin of species by variation 
and selection should grapple with the facts in detail, and show how the doctrine of the 
distinct origin and permanence of species will explain and harmonize them. It has been | | 
the diffieulty of limiting species is in propor- | 
Ka Oups or countries are more accurately known _ 
and studied in greater detail the limits of species become settled *. 
| | Foraminifera,’ he states that « there is À 
the range of variation has been studied — 
umber of specimens as have passed under 
Rupert Jones, and myself, in our studies of the — 
See Dr. J. E. Gray “On the Species of Lemuroids,” Proc. Zool. Soc. 1863, p. 134, : 
o 
EN. 
yc 0 
