PORIFERA. II. 



I 7 I 



ca. 30 mm ; the breadth of the leaf-shaped part is 24.'™, and the thickness ca. io mm ; the thickness of the stalk 

 is only r5 mm . Then we have specimens of decreasing sizes, the smallest one with a height of o, mm , of which 

 the stalk makes 2-5 mm , and the thickness of the upper part is 2 mm . All the specimens are attached to larger 

 or smaller stones. The colour (in spirit) is dirtily brownish gray. The consistency of the tissue itself is 

 soft, but the skeleton makes the sponge rather firm and elastic. On account of the peculiar softness of 

 the tissue, the sponge contracts much in drying, and also in spirit it seems to be highly contracted. The 

 surface is damaged in most specimens, so that its character cannot be decided from these specimens. 

 To judge from tolerably entire individuals, ends of fibres project, and in the protuberances formed in this 

 way spicules project; also the longitudinal fibres lying under the skin give rise to keel-shaped ridges se- 

 parated by grooves, so that the surface gets upon the whole a slightly grooved appearance. In undamaged 

 specimens a dermal membrane may be separated as a not especially thin, intransparent film. Pores 

 were not seen. Oscula: here and there, to be sure, a few scattered openings are seen, but these, I 

 think, are only due to damaging. In the best preserved specimen, on the other hand, a spout-shaped 

 osculum is found on the top of the sponge. It consists of a small, somewhat conical spout formed by 

 the dermal membrane; it has a height of iy™ and a somewhat similar breadth. In the spout, formed 

 by the dermal membrane, the dermal spicules are lying very close, parallel to the longitudinal axis. 

 In the other, less well preserved specimens, this osculum is not found, but everything indicates that 

 it has been present, some perpendicular canals being found in the upper part of the sponge, and some 

 thin-skinned parts with openings being seen in the uppermost edge. The mentioned specimen shows 

 only one osculum, but in other specimens several oscula seem to have been found. 



The skeleton. The dermal skeleton. The fibres running from the main skeleton to the surface 

 end in bundles of dermal spicules spread in a more or less penicillate way, which bundles cause the 

 projections of the surface and rise through them. As the fibres are not perpendicular on the surface, 

 but directed upwards, the projecting bundles are recumbent, when the dermal membrane is seen from 

 above. The dermal membrane, which is suspended between the projections, has, moreover, horizontal 

 dermal spicules, partly singly scattered, partly here and there in bundles. Besides, the membrane is 

 copiously provided with chelae. The main skeleton is of dendritic type. In the basal expansion spicules 

 are found closely packed without any order, but chiefly parallel to the uuderlayer. Towards the 

 middle they rise upward, and the expansion passes into the stalk. Neither are the spicules in the 

 stalk arranged quite as in a fibre, some of them being placed more or less obliquely; chiefly, however, 

 they are placed in the longitudinal direction. Especially in the central part of the stalk they are 

 directed longitudinally, while the more scattered arrangement is found in the peripheral layer; outer- 

 most a looser layer is found with spicules turned in all directions, and from this layer spicules project, 

 so that also the stalk becomes shaggy. Dermal spicules were not seen, either in the stalk or in the 

 basal expansion. Not till the stalk passes into the upper body, the spicules are arranged so as to 

 lie quite parallelly in the fibres. In the basal expansion and the stalk the spicules are shorter than 

 in the other parts of the body; upward in the stalk they become gradually longer. Where the stalk 

 passes into the upper body, it begins to divide, and the fibres continue up through the sponge, copi- 

 ously branching in a dendritic manner and also frequently anastomosing. Branches continually bend 

 out towards the surface, and end in the bundles of dermal spicules of the skin. All the fibres are 



