THE SPONGES. 



119 





latter in several directions in the shape of narrow elevated bands, which 

 are confluent with one another. 



r 



The color is a light yellowish-brown. The body is stony and incom- 

 pressible, and the interior is very dense. The surface appears smooth to 

 the eye, but is rough to the touch. With a lens the points of barely pro- 

 jecting radial spicules may be seen, distributed generally over the surface, 

 in some places thickly enough to form a nearly continuous furze, in other 

 places very scantily. Where the surface is uninjured it appears to the 

 eye, or with a lens, perforate with abundant minute rounded apertures 

 0.3 mm. to 0.5 mm. in diameter. These which at first sight seem to be 

 simple apertures, are the more conspicuous areas of membrane occupying 



the meshes of the dermal skeletal reticulum. They are more distinct in 

 Fig. 9, Plate 17, than in Pig. 12, Plate 17, simply for the reason that 

 the photograph from which the former figure was made, was taken from 

 the partially dried sponge, while in the other case the photograph was 

 taken from the sponge in alcohol. 



The pores are rounded, 50-80 /x in diameter. They lie in the meshes 

 of the dermal skeleton, one to a few in the mesh. In some of the meshes, 

 the dermal membrane exhibits no pores. In the cylindrical specimens, 

 rather numerous small rounded oscula, 0.7 to 1.0 mm. in diameter, are 

 scattered over the body, showing a partial arrangement in longitudinal 

 rows. In the two more or less plate-like forms, oscula similar to those 

 on the cylindrical specimens are scattered here and there over the surface 



without regularity of arrangement. 



Oxeas, Fig. 6, Plate 17. Spicule smooth, slightly curved, cylindrical 

 and then tapering at each end to a sharp point. Size, about 510 jjl x 32 fx. 

 Spicules are sometimes found divided at one end into three short diverging 

 branches. Rarely the spicule assumes the shape of a strongyle or style. 



Skeletal Arrangement. 



The main skeleton (Fig. 3, Plate 21, a section vertical to the surface) 

 is a reticulum of thick spiculo-fibres which are frequently indistinctly 

 outlined. The fibres are 300-600 /jl thick, consisting of many rows of 

 spicules, arranged for the most part about lengthwise in the fibre, and 

 packed together in a fairly close fashion. The spicules are united by a 

 small amount of spongin, which is insufficient, however, to give the fibre 

 a compact character. The superficial spicules of the fibre are only loosely 





