CALOAEEA. 39 



skeleton proper ; the gastral cortex is supported by the paired rays of the chiactines 

 and subgastral triradiates (see Fig. 120). The dermal cortex is formed of a thick layer 

 of irregularly scattered triradiates (Fig. 124). 



The oscule is shown in Fig. 121. There is a ring of small quadriradiates lying 

 tangentially round the inner edge, with short pointed apical rays from which sprin^gs 

 the diaphragm. There is a thick fringe of hair oxea, outside which there is an open 

 fringe of large oxea. The oscule is thick and the' flagellated chambers reach almost to 

 the edge. Near the oscule they are only in a single layer, but in the middle of the 

 sponge they are ten or twelve layers thick. 



Spicules (Fig. 123). 



Oxea. — There are four sorts of Oxea : — 



{a) Large projecting oxea, pointed sharply at the inner end, and very bluntly at 

 the outer end, which is thicker. Curved all along, more sharply near the 

 thicker projecting end. Length fairly constant about 700 ju,, thickness 30 /* 

 to 35 ju,. 



(6) Hair oxea, projecting in dense tufts, quite straight, length over 500 /x, 

 thickness about 1 ju,. 



(c) Minute spined hastate oxea, scattered all through the body-wall. Slightly 



bent, with the largest spines in a ring round the " set-over " of the spear- 

 head. Usual length 60 /u., occasionally 150 yi, thickness 4 /a to 5 ju.. 



(d) Small irregular oxea from the body-wall about 350 /x x 20 /a, often set-over 



in the middle of their length. 

 Triradiates.— There are two sorts of Triradiates :— 



{e) Large alate subgastral triradiates. Basal ray straight, tapering uniformly 

 to a sharp point, about 700 /x long x 16 /x thick. Paired rays equal, nearly 

 straight, 200jLtto320/x long X 20 /x thick ; oral angle 160°. 



(/) Smaller alate triradiates from the dermal cortex (probably the same as the 

 rare ones in the body-wall). These vary widely in size. Basal ray 

 straight, tapering uniformly to a sharp point, 170 ^ to 700 /x long x 10 /x 

 to 18 /A thick. Paired rays equal, forming a rounded bend at the centre, 

 but straight for the rest of their length, 120 /x to 270 /a long x 10 /x to 16 /x 

 thick. Oral angle very constant, 108° to 112°. 



(g) Chiactines. Basal ray straight, sharply pointed, 600 /x to 750 /x long x 14/a 

 thick. Paired rays bent more or less forwards, 200 /a to 280 fi long x 16 /a to 

 20 fx. thick. Oral angle variable, 135° to 160°. Apical ray about 80 /x x 12 /x. 



Oscular spicules. 

 (h) Large oxea like (a), but shorter ; 380 jx to 480 fx long x 18 /x thick. These 

 form an external fringe. The inner fringe is formed of hair oxea of 



unknown length. 



2 N 



