39 



It soon became clear that the loose upper part had been so much injured as 

 to render it impossible to ascertain how its contour was originally shaped. The 

 other characters, particularly those of its rather stouter central and basal parts, 

 could however be made out well enough. It was easy to discern that an annular 

 prominent ridge, about 1 cm. high, surrounds the sponge and divides the low 

 conical basal part, which is 23 cm. in diameter, from the larger upper cylindrical 

 part of the body. The summit of the sponge is much lacerated but the greater 

 part of it still present. The basal end, that is the apex of the cone forming the 

 lower surface, is truncate, slightly concave, and surrounded by a tuberculous ring- 

 wall a few millimeters high. It measures 3 cm. in diameter and is evidently the 

 place where the root-tuft has been torn off from the sponge. Several stumps of 

 basalia-spicules, as thick as knitting needles, protrude from it for a distance of a 

 few centimeters. The surface of the lower cone, outside this place of insertion 

 of the root-tuft, is strongly gyrated ; the gyri extend chiefly in a radial direction 

 and are frequently connected so as to form a sort of network, the meshes of 

 which are occupied by very irregular round cavities about a finger or a thumb 

 broad. The gyri extend nearly to the projecting annular ridge, only a zone 

 10-15 mm. broad, just within it, being free from the intervening cavities. 



The much larger and softer part of the body lying above the annular ridge 

 has a very different appearance. It most likely had in the living sponge the 

 shape of a low, terminally-truncated or shghtly-depressed beehive. Its trans- 

 verse diameter measures 22 cm. and it is about 18 cm. high. It was originally, 

 without doubt, entirely covered mth a dermal reticulation, which however is now 

 to be seen as a continuous net at the sides only ; above it has been much torn 

 and is quite defective. The meshes of this reticulation are numerous, rounded, 

 and on an average 3-10 mm. wide, the strands between them are much narrower. 

 In the vicinity of the annular ridge these meshes (holes) are smallest and least 

 numerous, upwards they increase in number and in size. The whole of this 

 reticulation is to be considered as a gastral or oscular sieve-plate. Below it, large 

 cavities are seen, which pass into wide, slightly-ramified, vertical canals in the 

 upper part of the sponge. These canals are closed above and emit terminally- 

 closed diverticula. Trabeculge connect the gastral reticulation with the tissue, 

 excavated by these cavities and canals, lying below. These cavities, some of 

 which are as large as a child's hand, communicate with the outer world freely 

 by the large apertures between the gyri on the*lower conical face of the sponge. 

 Through these apertures the water enters the cavities which represent the in- 

 current canal-system of the sponge. Between these incurrent cavities the excur- 

 rent cavities are situated. The latter are everywhere in open communication 

 with each other and with the subgastral cavity lying below the gastral reticula- 

 tion of the convex upper side of the sponge. Through the holes in the latter 

 the water leaves the sponge (pi. XXI, f. 1). 



