76 Annals Entomological Society of America [Vol. XIV, 
capsule and behind the mentum. In the insect shown in Fig. 27, it 
would appear that the ventro-median edges of the head capsule have 
become approximated, or ‘‘come together,’’ behind the narrow gular 
plate “‘gu,’’ and meet along the midgular suture ‘““mgs.’’ The fact that 
there is a narrow membranous space behind the gular plate ‘“‘gu”’ in the 
trichopterous larva shown in Fig. 20, while this space has apparently 
disappeared through the coming together of the median edges of the 
head capsule behind the gular plate ‘“gu’’ in the trichopterous larva 
shown in Fig. 24 (in which there is a midgular suture ‘““mgs”’ like that 
of the beetle larva shown in Fig. 27) would lend weight to the view that 
the midgular suture ‘‘mgs’’ is formed by the approximation of the 
ventro-median edges of the head capsule along the median line of the 
head. On the other hand, the midgular suture ‘““‘mgs”’ of Figs. 24 and 
27, may have been formed secondarily in the integument of the head 
capsule as the result of the formation of a midventral implex or infolding 
of the body wall, such as frequently occurs along the midventral line 
of the thoracic region. Comstock and Kochi, 1902, suggest that the 
midventral suture of the thoracic segments ‘perhaps represents the 
neural groove of the embryo;’’ but I am inclined to attribute another 
origin to the suture in question—which probably arose through the 
formation of an infolding of the body wall for muscle attachment. 
A study of the condition found in the different castes of termites 
throws some light upon the rather difficult question of the origin of the 
gular region, since in the termites, at least, the gular region appears to 
represent the posterior portion of an originally distinct plate which has 
become adherent to the head capsule. Thus, for example, in the head 
of a winged termite such as that shown in Fig. 13, the gular region 
“‘ou’’ forms the posterior portion of a distinct gulamental plate bearing 
the labels ‘‘gu’’ and ‘‘sm.”’ In the soldier caste of this same termite, 
on the other hand, the posterior portion of the gulamental sclerite 
(bearing the labels ‘‘sm”’ and ‘‘gu”’ in Fig. 16) becomes ‘‘soldered onto”’ 
the head capsule to form the gular region, ‘‘gu,’’ while the anterior 
portion of the gulamental area, bearing the label ‘‘sm,’’ remains free 
and forms the submental region. We may therefore conclude that in 
some cases at least, the gulamental plate (“‘gu’’ and ‘‘sm”’ of Fig. 13) 
becomes elongate and its posterior portion is more or less closely fused 
with the head capsule to form the gular region “‘gu”’ of Fig. 16. In such 
instances, the lateral margins of the plate in question may be rep- 
resented by the gular sutures on either side of the gular region “‘gu”’ 
shown in Fig. 16. 
The /abium or under lip is formed by the union of a pair of mouthpart- 
limbs (second maxilla) similar to the maxillary mouthparts. The 
statement so often made that the neck plates, or cervical sclerites, 
represent the labial segment whose appendages have left the neck 
region and have migrated into the head region to form the labium, is 
wholly false, and is unsupported by a single bit of anatomical or embryo- 
logical evidence. This matter, however, has been fully discussed in an 
article by Crampton, 1917, and need’ not be further considered here. 
