Sponge-fauna of Norway. 135 



tudinally, which have found their way down from the mus- 

 cular layer. It is through the pillars that the long-shafted 

 spicules pass on their way to the surface. 



The large elliptical cells of the underside of the muscular 

 layer are continued out of it down the sides of the pillars 

 and under the floor of the crypts. 



The cortex is traversed by the " intermarginal cavities " of 

 Bowerbank, or, as I shall term them, the " cortical funnels " 

 or "chouse"*. They consist essentially of a tube divided by 

 a sphincter into a shorter proximal and a longer distal part, 

 the " ectochone " and " endochone " respectively (PI. VII. 

 fig. 18, e). The ectochone is cylindrical or acutely conical for 

 the greater part of its length, its proximal end being either 

 the hemispherical termination of the cylinder or the rounded 

 apex of the cone ; its distal end is greatly expanded beneath 

 the dermal layer, and produced laterally into canals from 

 which smaller canals proceed and terminate in the pores of the 

 surface, either immediately or after once more subdividing into 

 still smaller canals. The endochone is a more or less hemi- 

 spherical dome, which may be prolonged downwards as a very 

 short cylindrical or conical tube, and which opens freely into 

 the subcortical crypt. Generally each crypt is furnished with 

 two or more funnels. The distal half of the ectochone lies in 

 the layer of trichite sheaves ; its proximal half and the whole 

 of the endochone lies in the muscular layer of the cortex. 

 The funnels are lined by an epithelial layer, outside which is 

 a layer of concentric muscle-fibres ; but when the ectochone 

 traverses the layer of trichite-sheaves, the concentric muscles 

 are replaced by gelatinous connective tissue containing fusi- 

 form corpuscles with nuclei. 



Arrangement of the Spicules. — The long-shafted spicules 

 which occur in the mark are chiefly robust acerates, gathered 

 together into loose fibres, which exhibit no regular arrange- 

 ment; on approaching the cortex, however, the fibres arrange 

 themselves along radii more or less at right angles to it, pass 

 through the pillars of the crypts, traverse the cortex, and 

 project beyond it. At the same time trifid spicules put in an 

 appearance, their distal triradiate ends lying imbedded at all 

 levels in the cortex, or expanding at some distance outside it. 

 Where the fibres pass out of the sponge their constituent 

 spicules have so much diverged from one another that the 

 fibre-like form is lost ; the dermal layer of the sponge is 

 slightly raised, tent-like, about the fibre where it emerges. 

 The small trifid spicules (PI. VI. fig. 7) are almost con- 



* x < * 3vr l' a funnel. 



10* 



