222: WILSON. [Vor. TX. 
of sponge tissue, the gelatinous tracts form a connected system 
in which run the main efferent canals. 
The dermal membrane, Pl. XIX, Fig. 66, contains numerous 
microscleres (oxeas), and the supporting brushes of tylotes are 
usually torn away with it. The pores are thickly distributed 
over most of the surface, but there are aporous or nearly 
aporous tracts found here and there. The pores lead directly 
into subdermal cavities, s. d.c., Figs. 61 and 64, which are in 
general smaller in the spongy regions than in the gelatinous 
(Fig. 61). Even in the spongy regions, Fig. 64, the subdermal 
cavities are surrounded by a certain amount of gelatinous 
tissue, there being very few flagellated chambers in their im- 
mediate neighborhood. The subdermal cavities, both those 
under the ridges and the furrows, communicate in an irregular 
fashion with one another and open into main afferent canals, 
af.c., Fig. 64, which, it will be seen from Figs. 61 and 64, 
enter the dense mass of flagellated chambers directly from 
above, and from the superficial portions of the gelatinous tracts 
as well. The main afferent canals subdivide, their terminal 
divisions opening laterally into the flagellated chambers, as is 
shown in Pl. XIX, Fig. 65 (af. c.), this figure representing a 
small portion of the mesoderm of Tedania, showing flagellated 
chambers and both afferent and efferent canals. The flagel- 
lated chambers open in the same manner into the efferent 
canals. The water passes out of the spongy tracts by numerous 
efferent canals distributed along the margin of the spongy and 
gelatinous tracts. These canals are well shown round the edge 
of several of the gelatinous tracts of Fig. 62. They open into 
the one or more larger vessels (main efferent canals) lying in 
the central part of the gelatinous tracts (Figs. 61 and 64, ef. c.). 
The main efferent canals have a denser wall than the rest, 
which is usually well provided with microscleres, arranged in a 
radial fashion. These canals communicate with one another 
and open at the oscula, as described above. The communica- 
tion of a superficial efferent canal with a deeper lying one is 
partly shown in Fig. 62, com. ef. c., the plane of the section 
cutting the connecting canal into two portions. The superficial 
efferent canals are especially interesting in the upper part of 
