Ml 
the-hands of the systematics of Lepidoptera, we have to fall back 
for an explanation of the phenomenon of heterotrope resemblance 
on the theories mentioned on pages 389 and 390. Let us shortly 
recapitulate what is required of the theories. Several distinct 
species as « models » occur side by side with a number of individual 
forms of a single species as « mimics ». The result of evolution is 
therefore very different in the « models » and « mimics », but there 
is nevertheless a close similarity in aspect between them. The 
theories have to answer the question, how has this resemblance 
originated ? 
Accident may play a role, but it is certainly a very insignificant 
role, since otherwise the instances of resemblance between Insects 
from different countries would not be so rare as they are. 
Although nobody can possibly deny that the course which evolu- 
tion takes ina species depends to a great extent on the constitution 
of the species itself, the theory of parallel or convergent develop- 
ment guided only by constitutional forces and only in one direction 
in a species (Orthogenesis) breaks down before the facts present- 
ed by systematics in the case of heterotrope resemblance. For the 
theory assumes: 1) that the individual form of the polymorphic 
species is as regards coloration a phyletic stage homologous to 
that occupied by the « model », which is erroneous, and 2) that the 
various individual varieties of a polymorphic species are stages of 
one line of development, which they are mostly not. Moreover, 
the theory does not explain the fact that these similarities, with 
few exceptions, occur in species which fly in the same district. 
The chemico-physical influence of the environment may be 
accepted as sufficient to account for the prevalence of a certain 
tone of colour in the species of a faunistic district, which is a phe- 
nomenon of frequent occurrence. The continued action of the same 
environment may also tend to render a variable species constant 
or a constant species variable. But it is inconceivable that the same 
chemico-physical influence on a species can break the species up 
into definite dissimilar forms which resemble each a distinct 
species living under the same influence. The theory maintains 
that the result attained in the species which resemble each other 
is the same; in this the theory is wrong. The individual forms of 
one species and a series of distinct species represent vastly different 
results of evolution. Systematics teach us that individual forms 
like fig. 310-354 have an utterly different standing in evolution 
from the species 31-35, the difference not being one of degree only 
but of kind. 
