SPONGES.-HALLMANN. ^67 



abundant longitudinally-directed (principal) spicules for the 

 most part arranged in close multispicular fibre-like strands, the 

 appearance and disposition of which is such that, at first sight, 

 they might be mistaken for main skeletal fibres, their resem- 

 blance to the latter being 

 heightened by the fact that 

 the spicules composing them 

 are held together by some 

 amount of yellowish spon- 

 ginous material. In addition 

 to these spicular strands, 

 however, though more or 

 less concealed by them ex- 

 cept towards the surface, 

 there is a reticulation of 

 longitudinal (main) and 

 transverse (connecting) slen- 

 der horny fibres with pauci- 

 serially-arranged coring, 

 and frequent echinating, 

 spicules ; the transverse 

 fibres are usually of not 

 more than a spicule's length. 

 Owing to the partial con- 

 cealment of the primary 

 fibres proper, by the dense 

 array of longitudinal spi- 

 cules, it is with the strands 

 which these spicules form, 

 rather than with the main 

 fibres, that the transverse 

 fibres appear to reticulate. 

 Finally, there are many 

 irregularly scattered princi- 

 pal and auxiliary spicules, 

 the former in greater abun- 

 dance. The general appear- 

 ance of the skeleton in this 



region of the sponge, as seen in longitudinal section, is not 

 unlike that of O. tenuis as seen in a marginal section parallel 

 to the plane of the sponge lamina — the multispicular strands in 

 the present case taking the place of the less closely arranged 

 "linear condensations" or "venations" of the latter species. 



The auxiliary spicules increase in number in the superficial 

 layer, and in some parts of it are very abundant ; they lie 

 generally parallel to the surface. Projecting beyond the sur- 

 face at the extremities of the main fibres are tufts of diver- 

 gently-arranged principal spicules— the terminal spicules of 



Fig. 57 — O. inornata. a Princi- 

 pal styli. b Auxiliary tylostylus. 



