32 2 WILSON. [\'0L. IX. 



of sponge tissue, the gelatinous tracts form a connected system 

 in which run the main efferent canals. 



The dermal membrane, PI. 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. 6i 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 PI. 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, cf. 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, t:07/i. cf. 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 



