Ant colonies > Internal structure of ants > Tactile Sensillae

Tactile Sensillae

Tactile (Trichodeal) Sensillae

As stated in a previous chapter, ants are usually covered with hairs, which are coarse and long on the body and shorter and denser on the legs and especially on the antennae. As all of these hairs are movably articulated to the general chitinous integument and are provided with fine nerve terminations, they are universally regarded as tactile sensillae, although they also aid in the removal of the larval or pupal skin during ecdysis, for they are at first bent at their bases and applied to the chitinous layer to which they belong, but later, in becoming erect, loosen and push the overlying exuvia away from the surface of the body. In section each hair is seen to be a hollow chitinous tube, closed at its apex and open at its base, which is bulbously swollen and fits into a ring-shaped thickening

FIG. 31. Trichodeal and campaniform sensillae of ants. (Janet.) A, Trichodeal sensillae from proximal border of fore coxa of female Lasius niger, X 1,000 ; B, single sensilla from the group represented in A, X 2,000 ; C, longitudinal section through tip of middle coxa, trochantec and base of femur of Myrmica rubra worker, X 100 ; D, cross-section of tip of hind tibia of M. rlrbra, X Zoo ; E, F and G, sections of cam­paniform' sensillae from tip of mandibles of M, rrrbra; H, campaniform sensillae near articulation of wing of female Carnponotrrs herculeanus, X 500 ; t, chitinous hair; c, chitinous integument ; h, hypodermis ; n, nerve-termination ; u, bell, or umbrella, in the center of which the nerve terminates ; x, groups of campaniform sense-organs; d, fossa or pit in the chitinous integument; p, pore in same.

of the chitinous integument (Fig. 31, A, B, Fig. 32, b ). This tube is secreted by one or more large hypodermal cells, and a delicate nerve fiber extends up into its base. When the tip of the hair touches an object the tactile impulse is evidently transmitted to the nerve through the movement of the bulbous base in its cup-shaped socket. There is, therefore, no essential difference between the tactile function of the hairs of ants and the analogous structure in mammals.