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122 



THE SPONGES. 



the short horizontal diameter, are about equal, and 7-8 mm. The sponge 

 is doubtless to be looked on as a ramifying form with subcylindrical 



predominantly, 



branches, the growth in this particular specimen being 

 although by no means exclusively, in one vertical plane. 



The color is brown, passing here and there into terra-cotta, as if that 

 were a remnant of the natural color. The sponge is hard, almost stony; 

 the canals large enough to give the interior a lacunose appearance when 

 cut across. To the eye or with a lens the surface appears finely reticulate, 

 the reticulum most evident over the larger canals. To the eye and the 

 touch the surface appears smooth, and in reality over much of it there 

 are no projecting spicules. Nevertheless there are plenty of places where 

 spicules project radially for a short distance in considerable number (Fig. 

 4, Plate 21). 



Rounded oscula, 2-3 mm. in diameter, are found at or near the ends 

 of the branches and on the protuberances. They are the apertures of 

 cylindrical cloaca-like cavities, the inner face of which both laterally and 

 at the bottom shows the openings of efferent canals. The cloaca-like 

 cavities are pretty deep, extending 4-8 mm. into the body of the sponge, 

 but are not continuous with one another. The pores are rounded, 

 60-80 /x in diameter, and lie in the meshes of the dermal reticulum ; 1 to 

 5-6 pores in a mesh. Pores are closed in some regions, but even then 

 perceptible as rounded darker spots, the rest of the pore area appearing 

 as lighter-colored trabeculae between the closed pores. This condition 

 of the closed pores is sufficiently distinct to appear in a photograph (x 30). 

 The flagellated chambers (Fig. 10, Plate 17) are somewhat flattened, 

 about 40 /x x 32 /x, and eurypylous. 



* 



Oxea, Fig. 10, Plate 17 ; smooth, slightly curved, cylindrical, 

 and then tapering at each end to a point. Size, 220 /x x 16 /x. 



Skeletal Arrangement. Main skeletal reticulum (radial section, Fig. 4, 

 Plate 21), in immediate neighborhood of the surface of the sponge, is 

 regular, with radial and tangential fibres. In the interior, reticulum is 



irregular, and with larger meshes. 



Fibres of the main skeleton are in 



general compact, although in spots they lose their sharp boundaries and 

 fade into one another. In such a spot there is no reticulum, merely a 

 mass of thickly scattered spicules. Fibres, 80-180 /x thick, averaging a 

 somewhat smaller size in the superficial region than in the interior. Tn 

 the superficial region the connectives are sometimes as thick as the radial 









