302 NEW YORK STATE MUSEUM 



dorsal cavities hare 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.Spc]. Then, if a section 

 is taken at the point hi [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 o,pvc, 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, vc, 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 into the 

 bases of the cavities like a wedge and completely closing them, 

 as was described above [pl.28, fig.8M;]. Figure 11 is a cross 

 section taken at about the point jJc of figure 8 and shows the 

 pair of marked cuticular thickenings which form tlie proximal 

 ends or bases of the paired ventral cavities, pvc, 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.lOs] 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 l-m of figure 8. It is located cephalad 

 of the spiracular opening and shows how the air ])assage, os, 

 extends cephalo-ventrad into the interior of the cuticular pocket. 



