1921] Crampton: Sclerites of the Head 79 
labial region bearing the labels “ pgr,’’ ‘‘Is,”’ “ prm,’’ etc., in the figures 
in question. The mentum ‘“mn”’ forms the second of the plates forming 
a series of three in the underlip region of the Neuropteron shown in 
Fig. 23, which I have taken as the basis for comparison with the higher 
insects. The mentum, “mn,” may be fused with the region ‘‘sm”’ 
behind it, as in the insects shown in Figs. 85, 86, etc. ; it may be separated 
from the submental region ‘‘sm” by a clearly defined mental suture as 
in Figs. 23, 26, 7, etc.; it may be demarked merely by a faint dividing 
line between it and the submental region as in Hig is yete.; or it may 
be a distinct plate ‘“‘mn”’ as in the insects shown in Figs: 823/77) 15,6, 
etc. In the insects depicted in Figs. 21, 31, 17, etc., the mentum is 
represented by a membranous area bearing the label “mn.” The 
mentales or small sclerites bearing a seta and situated in the posterior 
region of the mentum, ‘‘mn”’ of the caterpillar shown in Fig. 31, or in 
the trichopterous larve shown in Figs. 21, 20, etc., are possibly 
homologous with the chitinized areas in the posterior region of the 
mentum “mn” of the Neuropteron larva shown in Bigs 12; 
The eulabium comprises the distalmost, or anteriormost portion of 
the underlip region beyond the mentum, “mn,” from which it is sep- 
arated by a eulabial suture in the insects shown in Bigs 23,20 (27213. 
15, 17, etc. The eulabium, as was stated above, is the true labium, 
formed by the union of the second maxille. I would emphasize the 
fact that the labial appendages are homologous with the second maxillz 
of the Crustacea (see articles in bibliography) and it is wholly incorrect 
to maintain that the so-called superlinguz on either side of the hypo- 
pharynx of insects are homologous with the first maxillz (i.e. 
the maxillule) of Crustacea as is done by practically all recent investi- 
gators, since the “‘superlinguze’”’ are homologous with the paragnaths of 
Crustacea, and the labial appendages represent the true second maxillze 
of Crustacea, as has been brought out in a paper published in the 50th. 
Annual Report of the Ent. Soc. of Ontario, in a preliminary note in the 
Transactions of the Ent. Soc. of London; and in a more lengthy paper 
on this subject, illustrated by drawings of the parts in question in 
Crustacea and insects, which will soon be published in Psyche, and 
the Proc. Ent. Soc. Washington for 1921. 
As was mentioned in the preceding discussion, the greater portion 
of the sternum of the labial segment enters into the composition of the 
hypopharynx, or tongue-like structure on the floor of the mouth cavity. 
It is very probable, however, that the labiosternite or median triangular 
area between the bases of the structures labeled per’ in Fig; 10, 
represents a portion of the sternal region of the labial segment. The 
palpigers, “pgr,” or palpi-bearing structures on either side of the median 
triangular area shown in Fig. 10 (also structures labeled “per” in Figs 
6, 7, 15, 81, etc.) together with the labiostipes, “‘1s,”’ represent portions 
of the basal segments of the modified limbs forming the labium, while 
the distal segments of these limbs (representing the terminal segments 
of the ‘‘endopodite”’ of a crustacean limb) form the labial palpi “1p” 
of Figs. 6, 7, 10, 15, etc. Outgrowths of the basal segments “pgr’’ and 
“Is” of the limbs (these outgrowths possibly represent endites or ‘‘ gnath- 
