Cuaap. VI. ORIGIN OF NEW SPECIES. 133 
and shape as its sister kind, but differs very strikingly in colours: 
H. Melpomene being simply black with a large crimson spot on its 
wings, whilst H. Thelxiope has these beautifully rayed with black and 
crimson, and is further adorned with a number of bright yellow spots. 
Both have the same habits. H. Melpomene ornaments the sandy alleys 
in the forests of Obydos, floating lazily in great numbers over the lower 
trees ; whilst H. Thelxiope, in a similar manner and in equal numbers, 
adorns the moister forests which constitute its domain. No one who 
has studied the group has doubted for a moment that the two are 
perfectly and originally distinct species, like the hare and rabbit, for 
instance, or any other two allied species of one and the same genus. 
The following facts, however, led me to conclude that the one is simply 
a modification of the other. There are, as might be supposed, districts 
of forest intermediate in character between the drier areas of Obydos, 
etc., and the moister tracts which compose the rest of the immense 
river valley. At two places in these intermediate districts, namely 
Serpa, 180 miles west of Obydos, on the same side of the river, and 
Aveyros, on the lower Tapajos, most of the individuals of these Heliconi 
which occurred were transition forms between the two species. Already, 
at Obydos, H. Melpomene showed some slight variation amongst its 
individuals in the direction of H. Thelxiope, but not anything nearly 
approaching it. It might be said that these transition forms were 
hybrids, produced by the intercrossing of two originally distinct species : 
but the two come in contact in several places where these intermediate 
examples are unknown, and I never observed them to pair with each 
other. Besides which, many of them occur also on the coast of Guiana, 
where H. Thelxiope has never been found. These hybrid-looking 
specimens are connected together by so complete a chain of gradations 
that it is difficult to separate them even into varieties, and they are 
incomparably more rare than the two extreme forms. They link 
together gradually the wide interval between the two species. One is 
driven to conclude, from these facts, that the two were originally one 
and the same: the mode in which they occur and their relative 
geographical positions being in favour of the supposition that H. 
Thelxiope has been derived from H. Melpomene. Both are neverthe- 
less good and true species in all the essential characters of species ; for, 
as already observed, they do not pair together when existing side by 
side, nor is there any appearance of reversion to an original common 
form under the same circumstances. 
In the controversy which is being waged amongst Naturalists, since 
the publication of the Darwinian theory of the origin of species, it has 
been rightly said that no proof at present existed of the production of 
a physiological species,— that is, a form which will not interbreed 
with the one from which it was derived, although given ample oppor- 
tunities of doing so, and does not exhibit signs of reverting to its parent 
form when placed under the same conditions with it. Morpho- 
logical species—that is, forms which differ to an amount that would 
justify their being considered good species, have been produced 
in plenty through selection by man out of variations arising under 
domestication or cultivation. The facts just given are, therefore, of 
