94 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Surface views at Stage 3 (Figure 3) are given in Figures 9, 10, and 
LS dor: 
A sagittal section at this stage shows (Plate 3, Figure 13) an elon- 
gation of the labral fundament, and demonstrates its origin from the 
germ band by simple evagination. The posterior surface of the labrum 
is now the anterior wall of a distinct invagination (or.), the fundament 
of the stomodzeum. 
At Stage 4 (Figure 4) the labrum is longer (Plate 3, Figure 19, dbr.) 
and its long axis has swung backward, probably on account of the ex- 
cessive elongation of the anterior labral surface. A ventral aspect of 
the germ band (Figure 12) shows the labrum to be approximately oval 
in cross-section, but with a more rounded anterior surface. 
At Stage 5 (Figure 5) the labrum (Plate 3, Figure 20, br.) is de- 
cidedly longer. The basal part of the labral fundament represents the 
clypeus, with which the lateral folds, or mouth-folds (Figure 21, pli.or.) 
are now confluent ; overhung by the end of the labrum is the distinct 
stomodzeum. 
At Stage 7 (Figure 7) a distinct depression (Plate 5, Figure 31, dep.) 
separates the clypeus from the procephalic lobes ; the depression, in 
fact, may be seen as early as Stage 1, for it simply forms the angle be- 
tween the labral fundament and the procephalic lobes. Although the 
clypeus merges insensibly into the cheeks, the labrum is a free trapezoi- 
dal plate, as in the adult (Plate 6, Figure 40, dbr.). The antenne are 
now iuserted (Plate 4, Figure 24, Plate 5, Figure 30, at.) almost ex- 
actly opposite the base of the labrum. At this stage the clypeo-labral 
suture is not distinctly indicated (Figure 24), but in Stage 8 an invagi- 
nation occurs to form the labral hinge of the adult (Plate 6, Figure 40, 
ate.). 
In Stage 8 the only other important changes in the labrum are the 
evagination of single hypodermis cells to form the external sete, and 
the formation of trivial cuticular folds which represent the rudiments 
of the epipharynx. In Anurida, as in Orchesella, the epipharynx is 
purely a cuticular structure and unconnected with the central nervous 
system. 
In the adult Anurida a shallow clypeo-frontal groove is distinguish- 
able (Plate 6, Figure 40, su/.), but does not amount to a suture, and 
the clypeus is not laterally demarcated from the groove. In Orchesella 
and Tomocerus, however, the clypeus is a distinct sclerite. In none of 
the Collembola that I have studied is there any distinction between 
clypeus and labrum on the roof of the pharynx. 
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