162 THE MALAYAN PAPILIONIDE AS 
the great majority of cases, what we term “ species” 
are so well marked and definite that there is no dif- 
ference of opinion about them; 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 phe- 
nomena 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 
recently asserted by Dr. J. HE. Gray (in the Proceed- 
ings of the Zoological Society for 1863, page 184), 
that the difficulty of limiting species is in proportion 
to our ignorance, and that just as groups or countries 
are more accurately known and studietl in greater 
detail the limits of species become settled. This state- 
ment has, like many other general assertions, its por- 
tion of both truth and error. There is no doubt that 
many uncertain species, founded on few or isolated 
specimens, have had their true nature determined by 
the study of a good series. of examples: they have 
been thereby established as species or as varieties ; 
and the number of times this has occurred is doubtless 
very great. But there are other, and equally trust- 
worthy cases, in which, not single species, but whole 
groups have, by the study of a vast accumulation of 
materials, been proved to have no definite specific 
limits. A few of these must be adduced, In Dr. 
Carpenter’s ‘‘ Introduction to the Study of the Fora- 
