108 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 
thrown into a fold. In the overwintering generation, the larve hibernate, 
changing to pupa in spring without spinning cocoons. The characteristic which 
distinguishes the imagoes of this group from the usual type is that the dark 
scales appear on the outer edges of the white streaks and fasciæ; if a margin is 
present on an inner edge, it is much less pronounced. 
The wide geographical range and the large number of species would lead to 
the inference that the genus is an old one. If so, we would expect to find some 
species which have halted at an early stage in their evolution and have therefore 
preserved a color pattern which should bear some resemblance to the primitive 
one and hence afford a clue to it. Others would have advanced farther, develop- 
ment ceasing at different levels, so that the numerous differentiations produced 
should constitute a chain of related species, broken no doubt by numerous gaps 
but still sufficiently complete to indicate the different directions which evolution 
has taken. The problem of this research is, then, to determine what is the primi- 
tive color pattern of this group and knowing it to trace the paths along which 
evolution has proceeded in the production of the respective patterns of the 
numerous species now in existence. It is scarcely probable that the primitive 
pattern is preserved among any of the earlier genera from which Lithocolletis 
is descended. Such a long period of time has elapsed since the origin of Litho- 
colletis that the species now belonging to ancestral genera have probably deviated 
widely from the type of marking then characteristic of them. This view is 
rendered more plausible by the fact that the subgenus Cremastobombycia, which 
possesses structural generic characters which suggest it as the immediate ancestor 
of Lithocolletis, has a type of marking differing considerably from that common 
to the large and widely distributed typical group and resembling, to a marked 
degree, the type of marking characteristic of some of the species of the smaller 
and seemingly younger group, usually known as the ‘‘flat-larval group." If 
so, we should search for the primitive color pattern among the less differentiated 
species of the typical group of Lithocolletis. 
If evolution takes place in several definite directions irrespective of utility, 
as contended by Eimer, this group should offer an opportunity of testing this 
theory, within certain limits, since many of the highly specialized differentia- 
tions, indicating a high phylogenetic development and requiring a long time to 
perfect, are of almost microscopic proportions and of no conceivable value in 
the life of the organism. Hence it is improbable that natural selection would 
have stepped in to mar any results which might have been produced through 
orthogenesis. 
In a genus such as this, where the color combinations are relatively simple 
and the limits of the marks clearly defined and the pigmental colors belong to 
the single series of yellows (or reddish yellows), browns and blacks, the problem 
of tracing their differentiation both ontogenetically and phylogenetically should 
be one less complicated than in higher groups, and the observations should 
offer more direct testimony as to the means by which such results are obtained. 
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