FOLSOM: MOUTH-PARTS OF ANURIDA MARITIMA. 139 
rings, in each of which, in the more specialized insects, tergum, pleura, 
and sternum are present. 
In the head region of the Collembola, however, segmentation occurs 
only on the ventral side of the germ band. The entire gular region is 
labial in origin, and there is reason for regarding the clypeus as the 
tergite of the ocular segment. The mouth-folds are undoubtedly ex- 
panded pleura. Aside from these, however, it is idle to speculate about 
the location of other sclerites which are differentiated in more spe- 
cialized insects. Here, in the absence of such differentiation, it may be 
be said that the head-cylinder represents seven ideal rings, which dorsally 
and laterally are in no way demarcated from each other. Admitting 
that the procephalic lobes do extend backward and encroach upon other 
segments, the lobes may not be regarded as the tergites or pleurites of 
those segments, for they are simply thickened blastoderm, and increase 
in area in proportion as the blastoderm thickens ; but the convenience 
of applying a single term, “ procephalic lobe,” to either of these thicken- 
ings should not blind us to the fact that the lobe eventually represents 
the blastoderm of more than one segment. 
In the finished head (Plate 5, Figure 33) are certain elevated dorsal 
areas which, however, are not sclerites bounded by sutures, and are not 
clearly to be homologized with sclerites of other hexapod orders. The 
elevations referred to are directly correlated with underlying glands and 
muscles. 
The sides of the face in Apterygota, then, are homologous with the 
gene of Pterygota. In all insects the skull represents seven somites, 
but the cephalic sclerites of Pterygota, excepting labrum, clypeus, and 
labial sclerites, are not differentiated in the Apterygota. 
Tentorium. 
The tentorium of Anurida is essentially like that of Orchesella (Folsom, 
’99), consisting of a chitinous plate parallel with the frontal plane (Plate 
8, Figure 51, tvt.), from which diverge two pairs of chitinous arms (Plate 
6, Figure 35) extending to the skull: a dorsal pair (6r. d.) and a poste- 
rior pair (67. p.) embracing respectively the supra- and infra-cesophageal 
ganglion. <A third, or anterior, pair was found in Orchesella, but not in 
Anurida. 
Regarding the development of the tentorium in insects, most diverse 
opinions are held. After considerable study, I have come to the con- 
