Packard.] 
510 
[Feb. 19, 
wings, while (as in Callosamia promethea) the males with their 
larger wings, lighter bodies, broadly pectinated antennae, and con- 
sequently far keener sense of smell, could fly to a greater or less 
distance in search of their mates . 1 The principle of segregation 2 so 
well worked out by Mr. Gulick, to which Mr. Romanes’ theory of 
physiological selection is a closely allied factor, if not covering the 
same ground, would soon be in operation, and the tendency to breed 
only among themselves, rather than with the low-feeders, would 
more and more assert itself, until, as at present, arboreal moths, as 
a rule, almost, if not wholly, oviposit exclusively on the leaves or 
bark of trees. 
Comi ng now to the origin of humps, fixed or movable, and of spines, 
the change from herbaceous to arboreal feeding-grounds doubtless 
affected not only the shape of the body, causing it in many cases to 
be thick and fleshy, but also led to a hypertrophy of the piliferous 
warts common to all Lepidopterous larvae. The change was prob- 
ably not necessarily due to the stimulus of the visits and attacks of 
parasitic insects, because the low-feeders are, if anything, at the 
present day at least more subject to injury from them than arboreal 
caterpillars. The cause was probably more pervasive and a result of 
a change of the environment, such as is seen in the growth of thorns 
on desert plants, or the knees of the cypress and other water plants, 
or the aerial roots of orchids and other epiphytes ; and that they 
may have originated with comparative suddenness seems probable 
when we bear in mind the aerial roots of corn artificially produced 
in the lifetime of a single individual ; though it should be taken 
into account that plants are far more plastic than animals. 
If the reader will look at the recapitulations we have given at the 
end of the detailed life-histories of certain Notodontians, it will 
1 The secondary sexual characters so marked in Bombyces are perhaps the result of 
their peculiar arboreal habits; so also the apterous tendency of Orgyia and a few other 
forms, especially the arboreal Psychidae ( GEceticus and Thyridopteryx) as well as Ani- 
sopteryx and Hibernia. It may be questioned whether any wingless female Lepidop- 
tera live on herbaceous plants. Contrast with them the grass-feeding species of Noc- 
tuidse as those of Agrotis, Leucania , etc. 
2 In fact nearly the whole group of insects is an example on a vast scale of the prin- 
ciples of segregation, geographical isolation and physiological selection. As soon as the 
ancestors of insects acquired wings, their milieu was changed. The air rather than the 
earth became their habitat; the acquisition of wings introduced them to a new world of 
existence and free from the attacks of creeping enemies and other adverse conditions 
to which the terrestrial Myriapods and Arachnids were subjected ; the winged insects 
living a part of their lives, and the most important part, above the surface of the soil, 
multiplied prodigiously, the number of species being estimated by millions when we 
take into account the fossil as well as the living forms. 
