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.
3. The _Proboscis_, or _Haustellum_[1] (c), a tubular extensible organ
formed of the two maxillæ, or lower jaws, which have become greatly
elongated, semi-tubular, and closely pressed together at the edges, but
separable at the will of the insect--a structure which enables the organ to
be easily cleansed when necessary, and is extremely interesting as
indicating so clearly the true development of the proboscis from the
maxillæ.
The _Maxillary palpi_ (p.p) are two jointed organs attached to the base of
the proboscis and very frequently rudimentary, but fully developed amongst
certain of the _Micro-Lepidoptera_.
The _Labium_, or lower lip, is situated below the proboscis and carries the
_Labial palpi_ (figs. 5 and 6), two large jointed organs which are very
conspicuous in nearly all the species and often quite conceal the maxillary
palpi. They are usually regarded as organs of touch, but their true
function does not seem to be properly understood. In the _Lepidoptera_ they
appear to protect the proboscis, which, when out of use, is always coiled
up in a spiral between them. The labrum and mandibles can only be seen by
removing the large labial palpi.