COLEOPTERA. 
501 
The parts of the maxilla to which reference is most often made are 
the palpus and the galea. The number and form of the segments of 
the palpus are much used in descriptions; as is also the presence or 
absence of the galea. When the galea is developed as a distinct ap¬ 
pendage, the maxilla is said to be bilobed, the galea being termed the 
outer lobe % and the lacinia, or blade, the inner lobe (Fig. 604). When 
the galea is not developed so as to appear as an appendage the 
maxilla is said to have but one lobe. 
The intermediate portion of the labium is F, o c f - c ^~ Labium 
submentum; m, 
mcntura; jr, labial 
palpus; g, glossa, 
/, paraglossa. 
Much use is made of the form of the parts of the labium or lower 
lip in descriptions of beetles. When fully developed the labium con¬ 
sists of three principal parts and a pair of appendages. The principal 
parts are the submentum % the mentum, and the ligula ; the appendages 
are the labial palpi. The basal part of the labium, the part which is 
joined to the gula, is the submentum (Fig. 607, sin). 
By an unfortunate error this sclerite is almost in¬ 
variably described in works on the Coleoptera as the 
mentum. This fact should be borne in mind by the 
student when using any of the older books on this 
subject. 
the mentum (Fig. 607, ///); and the distal portion 
the ligula. The ligula is a compound organ ; but 
in beetles the sutures between the different sclerites 
of which it is composed are usually obsolete. Three parts, however, 
are commonly distinguished, a central part, which is sometimes 
divided at the tip, th eglossa (Fig. 607,^), and two parts, one on each 
side of the glossa, the paraglossa: (Fig. 607, p). The part on each side 
which bear the palpus is termed, when it is distinct, thepalpiger. 
The Thorax. —Each segment of the thorax is composed of several 
sclerities. The shape and relative position of these sclerites afford 
characters which are much used in classification. Figure 608 is a dia¬ 
grammatic representation of what is considered the typical arrange¬ 
ment of these parts in each of the thoracic segments. Each segment 
of the thorax is a ring, which is divided into four parts: a dorsal, a 
ventral, and two lateral. The dorsal part is named the notum (no'tum) 
or tergum (ter'gum); each lateral part the pleurum (pleu'rum); and 
the ventral part the sternum (stcr'num). 
When the notum or sternum of a particular thoracic segment is to 
be indicated, it is done by the use of one of the prefixes pro , meso , or 
met a. In this way are formed the terms pronotum , mesonotum , meta- 
no turn, prosternum, mesosternum and metasternum; which are applied 
to the nota and sterna of the prothorax, mesothorax, and metathorax 
respectively. 
/ 
