92 CEYLON PEARL OYSTER REPORT. 



nearly half, of an irregularly spherical sponge, about 35 milliins. in greatest diameter. 

 The surface is rather uneven, minutely hispid, and thinly encrusted with sand. 

 Neither pores nor vents are visible externally. The colour, in spirit, is grey, the 

 texture firm and compact and only slightly compressible. 



The skeleton consists chiefly of stout bands of oxeote spicules radiating from a 

 centrally (?) placed "nucleus" to the surface of the sponge. The outer portions of 

 these bands are often abundantly echinated by the cladi of the anatrisenes, lying 

 chiefly in the ectosome. 



Spicules. (1.) Protrisenes (Plate III., fig. 5, a) ; with rather short, stout cladi and 

 fairly stout shaft, tapering to hair-like fineness. Shaft about 276 millims. by 

 0-015 millim. (at the thickest); cladi about 0'054 millim. by 0'00625 millim. The 

 cladi may be slightly irregular, and I have seen one forked at the extremity. They 

 are sometimes much longer than in the specimen measured. These spicules occur in 

 positions similar to those of the anatrisenes, but are very scarce. 



(2.) Anatrisenes (Plate III., fig. 5, b, b'); with fairly stout, sharp-pointed cladi and 

 long hair-like shaft; length of shaft about 27 millims., of cladi about 0'058 millim. 

 Abundant. 



(3.) Oxea (Plate III., fig. 5, c) ; stout, fusiform, gradually and finely pointed at 

 each end; size about 2 '8 millims. by 0'046 millim. 



(4.) Sigmata (Plate III., fig. 5, d) ; slender, usually contort; very numerous, 

 especially in the walls of the inhalant canals ; measuring up to about O'Ol millim. 

 from bend to bend. 



(5.) Spherules ; smoothly rounded, but irregular in shape ; up to about 0'004 millim. 

 in diameter, but usually smaller. These bodies are enormously abundant in the 

 choanosome, but are practically absent from the ectosome. In the type specimen 

 they are thickly, but irregularly scattered; in R.N. 192 they are grouped in oval 

 clusters about O'll millim. in longer diameter. 



Stained sections show a fairly thick ectosome pretty sharply differentiated from 

 the choanosome and, to some extent, fibrous, but composed chiefly of chondrenchyme 

 with very numerous granular cells. The thickness of this ectosome, which almost 

 amounts to a cortex, in the type specimen, is about 074 millim. It is penetrated 

 here and there by narrow inhalant canals, leading almost vertically inwards from the 

 surface. The flagellate chambers are oval or nearly spherical, up to about 0'033 

 millim. in diameter. Their mode of opening and the arrangement of the excurrent 

 canal system have not been made out. The mesoderm of the choanosome ranges from 

 collenchymatous to chondrenchymatous. 



The extraordinary number of the siliceous spherules or globules in this sponge is 

 very remarkable. In R.N. 192 they are, as already stated, grouped together in oval 

 masses. They appear in this case to originate many together in special mother cells, 

 in which they first appear as very minute, highly refringent points. The oval groups 

 are probably still associated with the remains of the mother cells. The exact nature 



