71 



tween the head and the stem is as 1 : 3, it is here as 1 :.6 or 8; in other words the stem is 

 here proportionally double as long as in the H. boreale, and proportionally much thinner. 



Usually the stem exhibits a more or less strong but even curve on one side, and is 

 everywhere cylindrical, increasing quite evenly in thickness towards the base which often forms 

 a great enlargement (see tig. 46) at the place where the root-fibres begin to appear. This 

 part of the stem sunk in the ooze, and which may fitly be called the root, is curved in va- 

 rious ways; sometimes (see fig. 35) even in a right angle, but everywhere so thickly covered 

 with the numerous sinuous root-fibres full of extraneous matter, that its shape is often not 

 easily discernible. I have however always found that its extremity tapers again, and gradually 

 resolves itself into terminal root-fibres. 



As to the root-fibres themselves, they are of very solid consistency, and so tough 

 that they cannot be pulled asunder without difficulty. They are (fig. 41) rather transparent, 

 of yellowish color, and apparently in their interior of a perfectly homogenous compact struc- 

 ture. Usually they exhibit a cylindrical form, which is retained even under strong pressure; 

 they are variously contorted and ramified, and are everywhere covered with extraneous matter 

 of different sorts (Rhizopod-shells, siliceous spicula, grains of sand &c.) so adherent as not 

 to be entirely removed without considerable trouble. 



The body or head of the sponge (fig. 37) is club-shaped, with the upper surface more 

 or less flattened, yet most frequently so that such flattening is not at right angles with the 

 axis but somewhat oblique, From the highest side rises a very remarkable conical process 

 terminating in an opening, which is bounded by long projecting spicula and leads to the 

 interior of the sponge. This fistular process, which represents the out-flow aperture (osculum) 

 is usually situated on the edge of the head, so that its exterior side is flush with the side 

 surface of the head. Such I have found to be the case in nearly all the numerous specimens 

 from Lofoten which 1 have examined. Only in 1 specimen in which the head was unusually 

 thin and elongated, and probably on account of an accidental mutilation rather irregularly 

 shaped, the osculum was a little within the edge of the upper surface (here more directly 

 truncated) but still far removed from the centre. 



In the H. boreale there is also (at least in one of the specimens examined byLoven) 

 a single widely gaping out-flow aperture on the upper side of the head; but this aperture is 

 firstly not fistular nor prominent, and next, it is situated nearly in the centre of the upper 

 surface, which is also clearly the case in the specimen from Greenland before-mentioned, 

 which I presume belongs to the same species. 



The whole head is moreover everywhere hirsute with rather long projecting fine spi- 

 cula, which together form, in whatever position the sponge is viewed, a tolerably wide trans- 

 parent border around the head. These spicula projecting from the exterior skin are also 

 found in the H. boreale, but are proportionally shorter and less conspicuous. 



The color is greyish brown; in very small specimens much lighter or nearly yello- 

 wish white. 



