94 CEYLON PEARL OYSTER REPORT. 



constriction of the sponge below, the lower ends of these fibres approach the surface 

 almost without diverging from one another. 



(2.) More or less mingled with the foregoing in the lower parts of the sponge are 

 long, silky bundles of the very long, sinuous, hair-like shafts of anatrisenes, whose 

 heads echinate the bundles at varying distances beneath the surface. 



(3.) Dense surface brushes, composed partly of oxea which form the ends of the 

 long fibres and partly of protrisenes of hair-like thinness, whose cladomes project far 

 beyond the surface. 



(4.) Numerous oxea, much shorter than those of the fibres, scattered irregularly 

 throughout the body of the sponge. 



(5.) The root-tuft, composed of anatrisenes with extremely long and slender shafts, 

 irregularly matted together. 



Spicules. (f.) Protrisenes (Plate III., fig. 6, b.), (and diaenes) ; shaft and cladi 

 often of hair-like thinness ; cladi commonly of unequal length (one sometimes 

 suppressed entirely), projecting forwards at only a very small angle with the shaft. 

 In a perfect example in a boiled-out preparation the shaft is about 3"0 minims, long, 

 about 0'004 millim. thick just below the cladi, and tapering to hair-like fineness at 

 the other end. The longest of the cladi is about 0'05 millim. in length. 



(2.) Anatriasnes (Plate III., fig. 6, a); with extremely long, hair-like shafts, so 

 long and slender that they appear to be invariably broken off even in boiled-out 

 preparations, and I am therefore unable to give the measurements. The cladi are 

 fairly stout, gradually sharp-pointed, recurved at a very acute angle to the shaft, 

 and about - 04 millim. long by 0"004 millim. thick at the base. In boiled-out 

 preparations the shafts of these spicules stick together in silky wisps. 



(3.) Oxea (Plate III., fig. 6, c.) ; long and slender, commonly slightly curved, 

 very gradually and finely pointed, varying greatly in size according to position, 

 measured up to about 2"1 miHims. by - 01 millim. 



(4.) Sigmata (Plate III., fig. 6, d) ; slender and commonly contort, measuring about 

 0"008 millim. from bend to bend. Very numerous. 



The material is hardly sufficiently well preserved for minute histological investi- 

 gation, but the examination of sections prepared by the usual paraffin method shows 

 us the following features. There is no cortex and no distinct dermal membrane, the 

 ectosome not being sharply differentiated from the choanosome. The small inhalant 

 pores, scattered between the dermal brushes of spicules, lead directly into narrow, 

 elongated canals, which run inwards at right angles to the surface and unite below 

 the spicular brushes in larger inhalant canals which penetrate the deeper parts of the 

 sponge. The flagellate chambers are approximately spherical and about - 025 millim. 

 in diameter ; they are probably eurypylous. The exhalant canals are all narrow, 

 and converge towards the flask-shaped cloaca! cavities already mentioned. Numerous 

 large ova, many of them having very prominent pseudopodia, are scattered through 

 the choanosome. These ova measure up to about 01 1 millim. in diameter. They 



