3. Serrate, when the joints have sharp projections like the teeth of a saw. (Fig. 18, antenna of Melanchra composita.)
4. Filiform, when the whole antenna is simple or thread-like. (Fig. 19, antenna of Epirranthis alectoraria.)
The clothing of the antennæ also varies, and is distinguished as under:—
1. Ciliated, when clothed with one or two series of short, fine hairs.
2. Fasciculate-ciliated, when the hairs are collected into tufts. (Fig. 17, antenna of Chloroclystis plinthina.)
3. Pubescent, when the antennæ are clothed with uniform short hairs. (Fig. 19.)
The functions of the antennæ are still a matter of dispute amongst entomologists. The majority of the older naturalists regarded them as organs of hearing. The antennæ are almost always more fully developed in the male than in the female. From this circumstance many modern entomologists consider that one of their functions is to enable the former to find the latter.
The organs of the mouth are thus distinguished:—
1. The Labrum, or upper lip (Plate [I]., fig. 11, l), a minute rudimentary plate situated in front immediately above the proboscis.
2. The Mandibles, or upper jaws (m.m), two minute sickle-shaped organs situated just below the labrum, also rudimentary.