282 WILSON. [Vou. IX. 
and the smaller efferent, and in the body of the sponge it is 
not practicable to distinguish them. This arrangement of the 
canal system brings it about that the sponge body is cut up 
into narrow trabeculae, in which flagellated chambers are 
arranged in a single layer. 
The larger efferent canals are distinguishable without any 
trouble (ef. c., Fig. 2). They unite with one another and very 
often open into spacious cavities, just underneath the dermal 
membrane (here aporous), which are precisely like the sub- 
dermal cavities, only much larger. The membrane covering 
these oscular cavities is perforated by the oscular opening itself, 
which thus differs from a pore only in size. In Pl. XIV, Fig. 6, 
a portion of the surface is represented showing an oscular 
cavity, os.c., with an osculum, os. Looking through the oscu- 
lum, two efferent canals are shown, ef. c. Surrounding the 
oscular cavity are numbers of the conspicuous subdermal 
cavities, s.d@.c. Other and much smaller oscula are found, two 
of which are shown in Fig. 7, os. Such oscula seem to be 
nothing in the world but the openings of certain subdermal 
cavities from which the covering pore-membrane has dis- 
appeared. The canals into which such oscula open, branch 
very quickly, as is shown in Fig. 7. The oscula taken together 
are few in number, and are distributed over the surface with 
entire irregularity. They are not seated on elevations, and are 
inconspicuous. Nothing in their nature or surroundings could 
of itself warrant one in regarding them as a different type of 
structure from the pores. 
The flagellated chambers, 7. c., Fig. 2, are spheroidal, -and 
in the normal regions (those unaffected by the formation of 
gemmules) are closely set. The collared cells have small cell 
bodies, which stain but slightly, but have very characteristic 
deeply staining nuclei. The mesoderm in the normal trabe- 
culae is rather scanty. It consists of cells of many shapes and 
sizes, which however pass one into the other by slight grada- 
tions. As common a type as any is the rounded or amoeboid 
cell with a well-staining body, Pls. XIV and XV, Figs. 8 and 9. 
The body varies greatly in size, and these cells pass by insensible 
gradations into delicate spindle-shaped cells in which the body 
