[Illustration: Pl 2. EXAMPLES OF LEPTIFORM LARVAE.

EXPLANATION OF PLATE 2. Figure 1, different forms of Leptus; 2, Diplax;
3, Coccinella larva; 4, Cicada larva; 5, Cicindela larva; 6, Ant Lion;
7, Calligrapha larva; 8, Aphis larva; 9, Hemerobius larva; 10, Glyrinua
larva; 11, Carabid larva; 12, Meloe larva.]

[Illustration: Pl 3. EXAMPLES OF ERUCIFORM LARVAE.

EXPLANATION OF PLATE 3. Figure 1. Panorpa larva; 2, Phryganea larva; 3,
Weevil larva; 4, third larva of Meloe; 5, Chionea larva; 6, Carpet Worm;
7, Phora larva; 8, Wheat Caterpillar; 9, Sphinx Caterpillar; 10,
Acronycta? larva; 11, Saw Fly larva; 12, Abia Saw Fly larva; 13,
Halictus larva; 14, Andrena larva.]

[Illustration: 204. Tipula Larva.]

For reasons which we will not pause here to discuss, we have always
regarded the eruciform type of larva as the highest. That it is the
result of degradation from the Leptus or Campodea form, we should be
unwilling to admit, though the maggots of flies have perhaps retrograded
from such forms as the larvae of the mosquitoes and crane flies
(Tipulids, Fig. 204).

That the cylindrical form of the bee grub and caterpillar is the result
of modification through descent is evident in the caterpillar-like form
of the immature Caddis fly (Pl. 3, fig. 2). Here the fundamental
characters of the larva are those of the Corydalus and Sialis and
Panorpa, types of closely allied groups. The features that remind us of
caterpillars are superadded, evidently the result of the peculiar
tube-inhabiting habits of the young Caddis fly. In like manner the
caterpillar-form is probably the result of the leaf-eating life of a
primitive Leptiform larva. In like manner the soft-bodied maggot of the
weevil is evidently the result of its living habitually in cavities in
nuts and fruits. Did the soft, baggy female Stylops live exposed, like
its allies in other families, to an out-of-doors life, its skin would
inevitably become hard and chitinous. In these and multitudes of other
cases the adaptation of the form of the insect to its mode of life is
one of cause and effect, and not a bit less wonderful after we know what
induced the change of form.

Having endeavored to show that the caterpillar is a later production
than the young, wingless cockroach, with which geological facts
harmonize, we have next to account for the origin of a metamorphosis in
insects. Here it is necessary to disabuse the reader's mind of the
prevalent belief that the ter