INSECTS
the species as a whole. Independence entails responsibilities. A creature that leaves the beaten paths of its ancestors must learn to take care of itself in a new way. And
Fig. 152. The head of a tent caterpillar
A, facial view. B, under surface. C, side view. Ant, antenna; Clp, clypeus;
For, opening of back of head into body; Hphy, hypopharynx; Lb, labium; Lm, labrum; Md, mandible; Mx, maxilla; O, eyes; Spt, spinneret
this the caterpillar has learned to do preeminently well, as it has come up the long road of evolution, till now it possesses both instincts and physical organs that make it
Fig. 153. The mandibles, or biting jaws, of the tent caterpillar detached from the head
A, front view of right mandible. B, under side of the left mandible. a and p, the anterior socket and posterior knob by which the jaw is hinged to the head; EMcl, RMcl, abductor and adductor muscles that more the jaw in a transverse plane
one of the dominant forms of insect life.
The external organs of principal interest in the caterpillar are those of the head (Fig. 152). These include the eyes, the antennae, the mouth, the jaws, and the silk-spinning instrument. A facial view of a caterpillar's head shows two large, hemispherical lateral areas separated by a median suture above and a triangular plate (Clp) below. The walls of the lateral hemispheres give attachment to the muscles that move the jaws, and their size is no index of the brain-power of
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