LIBRARY

THE ANATOJV!:Y OF INSECTS 17
9. Clavate - club-shaped, in which the segments increase in diameter apically.
In HEMIPTERA, COLEOPTERA, LEPIDOPTERA, HY­
MENOPTERA.
10. Capitate - head-like, modified clavate type, in which the apical segments
form a distinct somewhat globose enlargement or knob. In
COLEOPTERA, LEPIDOPTERA, HYMENOPTERA.
11. Lamellate -leaf-like, modifted capitate type in which the enlarged apical
segments are lamellate and leaf-like and fold tightly or loosely together.
Greatly developed in the SCARABjEOIDEA.
12. Geniculate - elbowed type, in which the first segment or scape is elongated
and usually the longest of all; the second segment Or pedicel is
relatively short and variable in form; the remaining segments are variously
named the elm/a, clavola, or flagellum and comprise: the ring joints,
one or more small ring-like segments at the base of the clava; thefunicle
or series of small similar segments between the ring joints and the
club; the club or enlarged apical segments. Geniculate antennl:e are
common in the RHYNCHOPHORA, CHALCIDOIDEA, FORM 1-
COIDEA, and APOIDEA.
13. Aristate - modified form of capitate antennre, in which the large apical
portion terminates in a seta or bears a hair or arista which may be
naked or hairy. Common in D IPTERA.
Sensoria (sing. sensorium). - The sensoria or organs of smell are developed
on the antenna'! of most insects. They vary in size, shape, and numbers and
usually are much more abundant in males. They may consist of a circular or
oval pit or opening covered with a thin transparent membrane and are well
known in certain families of the HOMOPTERA. Sensilla are minute sense
organs of which there are many types consisting of cavities, cones or pegs,
domes, spines or bristles, plates, and rods, some of which occur in all orders
and are not confined to the antennre.
Compound or faceted eyes. - The most important organs of sight are present
in most adult insects and are situated one on each side of the head; divided into
a few or hundreds or even thousands of facets or small hexagonal areas, each
of which is a lens-like unit of sight known as an ommatidium. The numbers of
facets vary from six to nine in ants up to 28,000 or more in dragonfles (Tillyard,
Imms). The image is thought to be a mosaic pattern which specially permits
the perception of moving objects.
Ocelli (sing. ocellus) or simple eyes - small simple eyes common to both
immature and mature insects. In larVal of caterpillars they may be arranged
in a series on each side of the head, while in adults there are usually two
or three present, arranged in a triangle or row on the vertex as in many
dipterous and hymenopterous forms or two dorsally near the compound eyes
and one on the front or frons as in the case of grasshoppers, aphids, and
many others. They are thought to serve to distinguish a faint image and light
from darkness. Many larvre and adult insects have neither compound nor
simple eyes.