38 



PORIFERA. I. 



Tliis species is erect, and forms an oval leaf narrowed below at the place of attachment. The 

 height is 18"=™, the breadth has been ca. 10'=™ (the specimen is somewhat damaged), and the thickness 

 of the leaf is in the middle ca. 4*^% but it becomes somewhat thinner towards the edge which is 

 rounded. The leaf is slightly arcuate from the middle towards the edge, so that one side is somewhat 

 convex, the other somewhat concave. The consistency is soft and flexible. The surface is everywhere 

 final}- shaggy from the projecting spicules. The dermal membrane is thin, transparent, and without 

 spicules, it rests on the skeleton below, and is pierced by the ends of the fibres; accordingly there is 

 no special dermal skeleton. The colour (in spirit) is almost white, and the sponge is rather transparent, 

 only the longitudinal fibres are at the base seen to be yellowish. (The sponge is from a considerable 

 depth, and a large part of the tissue has probably been destroyed or quite washed away by the hauling 

 up). Pores are found rather densely on both sides as round openings; they are very much varying in size, 

 from 0.029 — 0-23""". With regard to oscula it has not been possible with certainty to establish their 

 behaviour, as the skin of the sponge only in few places is undamaged, and I have not been able po- 

 sitively to decide, whether they are to be found on both sides or only on one of them. In the skeletal 

 net cylindric holes or canals of a diameter of 0^5 — i'"'" are seen, lying rather close to each other; they 

 go in a horizontal direction almost through the whole sponge. If the sponge is viewed under a 

 magnifying glass, the oscular canals are seen to shine through on both sides, but they appear on both 

 sides. to be closed by the outermost net of spicules; according to this we should have to suppose that 

 the oscular openings are found on both sides either as one or as several pore-like openings for each 

 oscular canal; in this case there would be no difference of size between the largest pores and the oscula. 

 If, however, the layer of the skeleton closest to the surface is cut off on both sides and examined, we 

 shall here find a little difference between the two sides of the sponge, one side showing openings in 

 the net; these openings are situated over the oscular canals; I have not seen them surrounded by the 

 dermal membrane as distinctly limited oscula, but this I take to be due to the fact that the skin of 

 the specimen is not undamaged. In the specimen in hand these openings are sitiiated on the convex 

 side. If they are the oscular openings, these openings are thus exclusively, or at all events almost 

 exclusively, found on one side of the sponge, and considering the fact in the two following species 

 there can scarcely be any doubt that they are oscula. 



The skeleton forms a rather regirlar network with more or less rectangular or cubic meshes. 

 It consists chiefly of fibres running from the interior of the sponge arcuately upward and outward 

 towards the surface, which they meet at about a right angle. Accordingly the fibres spread in a 

 fanshaped manner both towards the surfaces and the edges of the sponge. The skeletal tissue forming 

 the inner or middle part of the leaf-shaped sponge, is, on account of this structure, less regular than 

 the part towards the surface. The mentioned fibres are imispicular; they are connected by spicules 

 that are more or less at a right angle to them, and only form incomplete fibres, which accordingly 

 run rather parallel to the surface. The first mentioned fibres pierce the surface to the length of a 

 spicule, and consequently the surface is finely shaggy, and there is, as has been mentioned, no parti- 

 cular dermal skeleton. Besides by this regular skeleton, the sponge is also supported by thicker, poly- 

 spicular fibres which from the base, where their thickness is greatest, branch up through the sponge; 

 they run as well in the middle plan of the sponge as towards the surface often crossing each other, 



