302 NEW YORK STATE MUSEUM 
dorsal cavities have entirely disappeared, and that the cuticle, — | 
while of about the same thickness, is not so strongly chitinized 
except around the periphery of the spine and the periphery of 
the ventral pair of cavities [pl.28, fig.5pc]. Then, if a section 
is taken at the point h-i [pl.28, figs. 2 and 8], it will be noted 
that the cuticular wall of the ventral side of the spine [pl.28, 
fig.6] is continuous with the body wall of the eighth abdominal 
segment, and that the ventral cavity is merged into the cavity 
at the base of the spine, while the ventral pair of cavities have 
moved nearer the dorsal surface of the spine, and the portion 
represented in figures 4 and 5, pve, as filled with hypodermal cells 
is at this point filled with cuticle, which completely fills the 
cavity. Figure 17 of plate 28 represents a sagittal section 
through the apex of the abdomen and through one of the caudal 
spines, cs, the section passing mesad of the spiracular opening. 
At the base of the spine should be noted the cuticular pocket, 
cp, which extends into the paired ventral cavities at the base 
of the spine, and the thick layer of hypodermal cells, hep, sur- 
rounding the cuticular pocket. The base of the spine and its 
related portions are shown at figure 8 still more enlarged. The 
section from which this figure was drawn was taken laterad 
of the spiracular opening. In this figure should be noted like- 
wise the paired ventral cavities, pvc, the ventral cavity, ve, and 
the cuticular pocket, cp. It shows also the intimate relation 
existing between the paired ventral cavities and the cuticular 
pocket, the cuticular wall of the pocket extending inte the 
bases of the cavities like a wedge and completely closing them, 
as was described above [p].28, fig.8w]. Figure 11 is a cross 
section taken at about the point j-k of figure 8 and shows the 
pair of marked cuticular thickenings which form the proximal 
ends or bases of the paired ventral cavities, pve, the large cavity 
contained between and around the cuticular thickenings, and 
the caudal part of the spiracular opening, which in this sec- 
tion does not communicate with the exterior. The spiracle 
opens directly at the base of the spine [pl.27, fig.19s] and ex- 
tends from the surface in a cephalo-ventral direction into the 
cuticular pocket. On plate 28, figure 10, is shown a section 
cephalad of the one just described, which shows the external 
communication of the spiracle and the heart-shaped cuticular 
mass which forms the cuticular pocket, the heart-shaped form 
being derived by the gradual extension of the cuticle into the 
cavity lying between the cuticular thickenings forming the bases 
of the paired ventral cavities. Figure 13 represents a section 
taken at about the level I-m of figure 8. It is located cephalad 
of the spiracular opening and shows how the air passage, 0s, 
extends cephalo-ventrad into the interior of the cuticular pocket. 
