136 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the mandibles in rate of downward growth, and the lateral surface of 
the mandible to be concave, in conformity with the swollen distal region 
of the mouth-fold. 
In Stages 6 and 7 (Plate 1, Figure 6; Plate 2, Figure 7) the folds in- 
volve the labrum and second maxille (Plate 4, Figure 24; Plate 5, Figure 
30, pli. or.), covering the mandibles and first maxillee laterally, and form- 
ing the genze, or sides of the face. As seen in Stage 7 (Plate 5, Figure 
30), each oral fold connects one side of the clypeo-labral fold with the 
labial evagination of the same side. There are no sutures, however, to 
indicate the union of the genz dorsally with the clypeus and ventrally 
with the second maxilla, for the oral evagination, in its backward and 
forward extension, has at length involved the labial and clypeal folds, 
respectively, in such a way that all three folds become one and enclose 
a single common cavity. The anterior margin of the mouth-fold is still 
distinguishable, however, as late as Stages 7 and 8 (Plate 4, Figure 24, 
pli. or.) ; the mesal surfaces of the labial fundaments have not united 
anteriorly (Plate 5, Figure 29); the labrum is free from the fold (Figure 
30) and remains so. The mouth is definitely bounded, but still open 
(Figures 30, 34) ; its closure occurs, however, before the egg hatches. 
The folds — clypeo-labral, oral, and labial — have been converging con- 
comitantly with their elongation, and continue to elongate and converge 
until they meet to form a buccal cone, which completely encloses the 
inner mouth-parts. After hatching, there is, for reasons just given, no 
demarcation of the mouth-fold ; it can simply be said that the region 
designated as pl. or. in Figure 40 (Plate 6) is the anterior part of that 
fold. Also in Orchesella the corresponding region, under which project 
the palpi (Folsom, ’99, Plate 2, Figure 9), doubtless originates as in 
Anurida, but the clypeus is not confluent with the folds. 
Strictly speaking, then, the mandibles and maxille are not “‘ retracted,” 
as is usually stated ; but they are overgrown by the gene. 
Hansen (’93, p. 208) wrote concerning Campodea, Japyx, and Collem- 
bola, ‘die Mandibeln und Maxillen, mit Ausnahme der Spitzen, ‘im 
Kopfe liegen.’ Dieses ist dadurch entstanden, dass sich die Haut hinter 
ihrer Einlenkung wie eine Duplicatur, welche Gewebe enthalt, vorwarts 
und um sie herum gefaltet hat, und die Rander dieser Duplicatur sind 
auf der Unterseite des Kopfes mit dem Seitenriindern des Labiums 
festgewachsen, so dass dieses fast seiner ganzen Linge nach mit der 
Seitenwand des Kopfes verbunden ist.” These facts he ascertained by 
laborious dissections of the finished parts. 
Packard (71, p. 21) simply mentions that “ the cephalic plates, which 
