530 MR. H. W. BATES ON THE LEPIDOPTERA 
further to the west, the species was again extremely variable, but the varieties were 
quite different from those of Ega : individuals coming very the near type occurred, but 
not one was fonnd quite conformable. M. Egaensis was quite absent ; but, on the other 
hand, a new variety abounded at St. Paulo, of which there was certainly no trace at 
Ega ; this has been figured and described as a distinct species, viz. M. Mazceus (Hewits. 
Exot. Butt. Mechanitis, fig. 8). Two other remarkable varieties also occurred — one near 
M. Menophilus (Hewits. 1. c. Mechanitis, figs. 2, 3), and the other with a structural 
modification in the shape of the wings, described below as M. Olivencia. 
The way in which I found this species to vary, as just described, impressed me greatly, 
and helped much, in conjunction with other facts of a similar tendency, not only to 
destroy my belief in the constancy of species, but to teach how new ones may have 
originated. The complete set of connecting forms found showed that I had here to deal 
with one species only, disseminated over a large area, and modified in certain districts 
under peculiar conditions there obtaining. The varieties were of such a nature as to 
form and colours, that it was inconceivable they could have been hybrids produced by 
the intercrossing of two or more originally distinct species. The amount of local 
modification exhibited was not in accordance with . obvious differences in the local 
conditions ; for the species was totally changed from Ega to St. Paulo, 260 miles apart 
and very similar in soil, climate, &c, whilst very constant on the Lower Amazons, in 
districts 600 miles apart and very different in physical conditions. Since returning 
to England, I have learned that M. Tolymnia again varies on the eastern slopes of the 
Andes, whilst a cluster of remarkable varieties or local forms (some of which have been 
described as species) are found in the Andean valleys. Some of these (M. Macrinus, 
M. Menophilus, &c.) are very clearly varieties of M. Polymnia, like the forms found at 
Ega and St. Paulo ; but others ( M. Mothone, M. Menapis) are more sharply defined, and 
have the appearance of true species. Now I think the conclusion is unavoidable, that 
these apparently distinct species are modifications, as well as the undoubted varieties are ; 
tor we have the species in all stages of modification — simple variation, local variety 
scarcely distinguishable from a mere variation, complete local variety, and well-marked 
race or species. The forms of M, Polymnia found in South Brazil confirm this view. 
At Bio Janeiro the well-marked race or species M. Jjysimnia alone is found ; at Bahia 
(travelling towards the home of the type, M. Polymnia), M. Jjysimnia in company with 
M. Nescea, a form exactly intermediate between Jf. Polymnia and M. Lysimnia; at 
Pernambuco (further northward) M. Nescea alone occurs ; at Para this form is seen no 
more, and M. Polymnia in its typical dress monopolizes the field. 
These facts seem to teach that, in this and similar cases, a new species originates in a 
local variety, formed in a certain area, where the conditions are more favourable to it 
than to the typical form, and that a large number of such are simultaneously in process 
of formation from one variable and widely distributed species. The new species cannot 
be proved to be established as such, unless it be found in company with a sister form 
which has had a similar origin, and maintaining itself perfectly distinct from it. Cases 
of two extreme varieties of a species being thus brought into contact by redistribution 
or migration, and not amalgamating, will be found to be numerous when the subject is 
