282 IVILSOX. [Vol. 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 PI. 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, cf. 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, /. 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. Pis. 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 



