the Larva of the Noctuae.
21
I propose to deal only with the question as to the affinities of
the Geometrae and Nocture, since, in the case of these two
groups, materials have been accumulating for some years,
which, in my opinion, enable us to give a definitive answer
to the question of their relative positions.
Before entering into details, I may just call attention to
the differences in structure between the caterpillars of the
Nocture and of the Geometrae.
A perfect Lepidopterous caterpillar is composed of thirteen
segments, counting the head as the first, and possesses
altogether sixteen legs, the three foremost pairs being the true
or thoracic legs, which correspond with the legs of the perfect
insect. The thoracic legs are horny, and are situated on the
2nd, 3rd, and 4th segments. The other legs, which are
fleshy, are known as the abdominal legs, prolegs, or claspers,
and are situated on the 7th, 8th, 9th, 10th, and 13th seg-
ments. The larva? of the butterflies, Sphinges and Bom-
byces, have the full number of legs; the caterpillars of the
Geometra?, on the other hand, have, as a rule, only four
claspers, one pair on the 10th and 13th segments, so that in
walking they arch their backs in the peculiar manner so
familiar to us, and which has given rise to the name of
"geometer" or "looper." Some few exceptions occur
among the Geometra?, such as Rumia Crataegata and Odontopera