SPONGES— KALLMANN. 



123 



compactness of the skeleton generally, the sponge is (in the 

 dry state) fairly hard and incompressible. The dimensions 

 of the specimen are as follows: — Height, 100 mm. ; depth of 

 cup, 40 mm. ; average thickness of 

 cup-wall, 15 mm. ; principal internal 

 diameters of cup, 120 mm. and 30 

 mm. No oscula are visible to the 

 naked eye. The surface, however, is 

 pierced by minute circular openings 

 40 to 50 fi in diameter and, on an 

 average, about 250 n apart. In a 

 thick vertical section, cut trans- 

 versely through the cup-wall, two 

 regions are roughly distinguishable : 



(i 



A superficial layer varying 

 from I mm. to 4 mm. wide, 

 in which the spicules are 

 not at all collected into 

 strands, but are closely 

 crowded without recognis- 

 able order except in some 

 parts of its outer limits, 

 where the majority of the 

 spicules may stand more or 

 less perpendicularly to the 

 surface. 'i'he spirasters, 

 which are plentifully scat- 

 tered throughout the whole 

 sponge, become more and 

 more closely aggregated as 

 the surface is approached, 

 and ultimately produce, by 

 their close crowding, a 

 dense and compact thin 

 external crust. 



(ii.) An extensive central region 

 traversed bv irreg-ularlv 

 s 



sinuous, ascending "fibres" Fig. 22-5. poculoides 

 or "columns" composed of a Tylostyle. a Ditto 

 loosely associated spicules. basalextremity). b Spi- 

 In the section the rasters, 

 "columns" appear to be 

 discontinuous, owing pro- 

 bably to their passing out of the plane of section. 

 They sometimes broaden out into diffuse bands, 

 sometimes contract into more compact strands. The 



