FAUNA OF THE OUTER WESTERN AREA OF THE CHANNEL. 311 



(a) A primary interlacing network, ramifying through all parts of 

 the sponge, of very clearly defined (? keratose) fibres, each composed of 

 bundles of fibrillae, and commonly enclosing a variable number of 

 oxeote spicules running longitudinally within them. Sometimes the 

 enclosed spicules are very numerous, but often they are entirely absent 

 from the fibres. In a tangential section of one specimen some of the 

 larger fibres attain, even close to the surface, a thickness of as much 

 as 100 ju. In a tubular portion of the same specimen a thick fibre 

 traverses the centre of the tube, throwing off subdividing branches to 

 the periphery. Oxea occur likewise, though with extreme scarcity in 

 this axial fibre and even in its slender branches to the wall of the tube. 

 (h) A secondary Beniera-like, and to some extent regularly disposed 

 network of unispicular meshes, with a decided tendency to assume in 

 the main lines an outwardly radiating direction from interior to surface. 

 This appears to be quite independent of the primary network. The 

 ends of the spicules are cemented together with deposits of spono-in, 

 usually to a distance of about 20 /m. down the shaft from the point. 

 The spicules composing this network are oxea of fairly uniform dimen- 

 sions averaging about 90-100 ju. in length by 5 /j. in width. With 

 them are associated, irregularly disposed, smaller oxea of about the 

 same length, and half or less than half the width, and very fine hair- 

 like oxea of about 50-60 fx by 1 /ul. 



The spicules of the primary skeleton are similar in form and dimen- 

 sions to those of the secondary skeleton, and include the slender hairlike 

 forms of the latter. The dimensions of the large oxea shown by Bower- 

 bank's figure for the species are rather larger — about 124 /m by 6*5 //. 



The tubular tendency of the sponge seems to place the 

 species in the genus Siphonochalina as defined by Schmidt (33, 

 p. 7), and by Pddley and Dendy (31, p. 29); but the remark- 

 ably composite structure of the fibres of the primary skeleton, 

 very different from the clear fibres of, e.g., Chalina oculata, leaves some 

 doubt as to its identity with the species to which it is here assio-ned, or 

 indeed of its true position among the Chalininae. The fibrillae of which 

 the fibres are composed have themselves individually the form of a 

 string of beads, each bead contributing internally a separate rod- 

 shaped element to form a centrally-placed strand running alono- the 

 string. Loisel * describes an almost identically similar condition in cer- 

 tain species of Rcniera, so called. But in the present examples I find no 

 evidence of the bead-like cells which secrete the elemental rods ulti- 

 mately breaking down, as Loisel describes, so as to have a simple con- 



* Contribution a rhistophysiologie des iponges. Journ. de I'anat. et de la ph)-siol 

 XXXIV. 1898. 



