1925] External Anatomy of Head and Abdomen of the Roach 203 
the other side of the maxilla, and is therefore not well shown in 
the view of the maxilla drawn in Fig. 2. The palpifer pf is a 
destinct sclerite in lower insects and bears the galea ga, but in 
the roach the palpifer becomes rather closely united with the 
stipes stj and the stipes appears to bear the galea, although if 
one examines the other surface of the maxilla, the connection of 
the basal portion of the galea bg with the palpifer pf is more read- 
ly apparent. The galea ga is composed of two segments, the 
basigalea bg and the distigalea dg, and the distal segment dg 
forms a sort of hood into which the tip of the lacinia is received. 
A strengthening rod gb (Fig. 3) stiffens the galea on its mesal 
surface (the one which fits around the tip of the lacinia) and 
a marginal region pga (Figs. 2 and 3) of the galea is clothed with 
fine hairs. The maxillary palpus mp is borne by the palpifer pf 
and is composed of five segments. The terminal segment is 
membranous at the tip and is provided with sense organs. 
The labium or underlip of the roach articulates posteriorly 
with the sclerite labelled tf in Fig. 11, and the sclerite in question 
probably represents the dorso-lateral portions of the labial seg- 
ment, according to the investigations of Holgren, 1909. The 
basal sclerite sm of the labium (Fig. 11) is made up chiefly of 
the submentum, although its posterior portion may contain the 
gular region of other insects such as soldier termites, Coleoptera, 
etc. On the other hand, the gular region may form behind the 
submentum, and the origin of the gular region is still a matter 
of doubt. The gular pits gp of Fig. 11, which are usaully situated 
on the gular sutures demarking the gular region laterally, are 
hidden by the postero-lateral edges of the submentum sm in 
Fig. 11. These gular pits are the external manifestations of 
the invaginations forming the posterior arms of the tentorioum 
(Fig. 13 pot ) as was mentioned above. 
In front of the submentum sm is the mentum mn (Fig. 11), 
and the entire region in front of the mentum mn is referred to 
as the eulabium, because it is the only part of the underlip formed 
by the union of the labial appendages in termites, according to 
Holmgren, who maintains that the mentum and submentum 
are formed behind the labial segment in the embryo. In front 
of the mentum mn is a small median triangular region il or in- 
