48 



reticulation described above. Their convex distal ends protrude into the sub- 

 dermal cavities and the incurrent canals, which appear as narrow continuations 

 of the latter. 



The main supporting skeleton appears as a tubiform network, which lies 

 close and parallel to the inner (gastral) surface of the tubular sponge. The 

 strands or beams composing it are about 300 /^ thick. Its meshes are rectan- 

 gular, often quadratic and 2-3 mm. wide. The strands consist of the rays of 

 the stout principal stauractines and the slender comitalia attached to them, which 

 are parallel and close together and form dense bundles. These stauractines are 

 the largest spicules of the sponge. Two opposite rays of each stauractine 

 extend transversely, the other two longitudinally. The former are on an average 

 5, the latter 10-12 mm. long. The rays are, near the centre of the spicule, 

 about 100-150 i^ thick (pi. IX, f. 8) and gradually attenuated towards the sharp- 

 pointed end. The rays of the comitalia are 6-12 m thick and as long as those 

 of the principalia to which they are attached. The free ends of the comitalia- 

 rays are conically pointed, often a Kttle thickened, and generally covered with 

 small tubercles or spines. Most of the comitalia are sagittal triactines with 

 lono-itudinally-extending paired rays ; the unpaired ray is vertical to the other 

 two and extends transversally. It may be straight and form part of a trans- 

 verse bundle in its entire length (pi. IX, f. 9), or it may be abruptly bent under 

 a rio-ht-ano-le near its origin and form part of the same longitudinal bundle in 

 which the two other rays lie (pi. IX, f. 10). Also diactine comitalia are very 

 numerous. Both these and the triactine comitalia possess rudiments of the 

 missino- rays of the ideal hexactine, which appear as small tubercles or rounded 

 protuberances (pi. IX. f. 9, 10). 



Among the principal parenchymalia numerous macrosclere oxyhexactines with 

 gradually attenuated rays, 500-1000 /^ long, are also met Avith. These lie in a 

 sino-le layer outside the main skeleton-net, two opposite rays being vertical to 

 the axis of the sponge. The radial rays of the hypodermalia attach themselves 

 closely to the distal, radial rays of the parenchymal oxyhexactines. 



The hypodermalia and hypogastralia require a detailed description. Both 

 are reo-ularly arranged in equidistant transverse and longitudinal rows and 

 form a very graceful mosaic. The freely projecting distal hypodermalia- and 

 proximal hypogastralia-rays are usually accompanied by one or more slender 

 diactine comitalia. The stout distal rays of the hypodermalia protrude freely 

 from the outer surface, which is raised in the shape of small cones at the points 

 of eo-ress of these rays. They are about 230 /^ long, slightly thickened in a 

 spindle-shaped manner above the middle, and end with conic points. Basally 

 they are smooth, further up covered with low, oblique spines pointing outwards. 

 The proximal ray is not quite so thick as and is considerably longer than the distal 

 ray. It measures 500 h- and more in length, is smooth, and gradually attenuated 



