I04 PORIFERA. II. 



seen in the dermal membrane, and were measured to a size of ca. o'oa""". They are only observed 

 with difficulty, the outer layer of tissue having the character of very small subdermal cavities situated 

 within each other and separated by membranes, and the pores piercing only the very outermost mem- 

 brane. From the subdermal cavities cylindric canals continue inward which canals may be observed, 

 when a piece cut off parallel to the surface is regarded from the inside. Oscula: Separate great 

 oscular apertures are not to be found, but it is likely that the papillae carry the excurrent openings, 

 as the inner tissue between the central axis and the outer layer is lacunous, and canals are running 

 longitudinally in the papillae, partly in the tissue between the axis and the outer layer, partly as 

 sharply and distinctly bounded canals in the outer layer. Outermost in the terminal part of the 

 papilla a cavity is found, or the middle part of the head of the papilla consists of a somewhat lacunous 

 tissue without spicules. Now the end of the papilla is copiously provided with poreshaped openings, 

 and as I suppose the said canals, at all events those running in the inner tissue, to be excurrent 

 canals, I suppose the openings in the terminal part of the papilla to be excurrent ones. 



The skeleton consists of a strong axis running through the middle of the sponge, and also 

 continuing into the branches of the root. The axis is not quite compact, but is composed of a number 

 of close-lying, strong fibres. In its lower part the axis is spirally twisted; this twisting is here very 

 distinct to the naked eye, as it is not the spicules of the single fibres which are spirally arranged, 

 but it is the whole, of fibres composed stalk that is twisted, so that it gets some resemblance to a 

 rope. In the single fibres, on the contrary, the spicules are placed in the longitudinal direction of the 

 fibres without any twisting. The twisting is most marked in the lower part of the stalk, but upward 

 it becomes less marked, and at last it is lost; it disappears also in the root-branches. In the largest 

 specimen the thickness of the spicula-axis is ca. i4 ,nm . Through the middle of each papilla runs a fibre, 

 which is formed by one of the fibres composing the axis bending off and passing through the papilla. 

 Where the fibre bends off from the stem it is supported by some spicules placed in the angle and 

 reaching to the middle of the stem. The papillae evidently correspond to the branches of the Clado- 

 /■///iff-species. The skeleton of the other parts of the sponge supports the layer of tissue that coats 

 the axis and its branches, i. e the papillae. In the crusty outer layer this skeleton consists of a very 

 dense layer of needles lying irregularly in all directions. Part of the spicules project through the 

 surface and makes it shaggy. Down on the stalk the la)er of tissue consists only of this outer, firm 

 part, and it is easily separated from the stalk. In the thicker part of the body, on the other hand, 

 the crusty layer passes inwardly, with a more or less indistinct bordering, into the soft, more lacunous 

 layer of tissue nearest the axis which layer is provided with fewer spicules, partly scattered, partly 

 gathered in bundles or shorter fibres. Also here the whole layer may be easily separated from the axis. 

 Down on the stalk the crusty layer is about 2 mm thick, higher up in the expanded part it reaches a 

 thickness of 3— 5 mm . In the papillae the construction of the skeleton is the same; in a transverse or longi- 

 tudinal section the fibre is seen in the middle, then a soft layer with fewer spicules, and outermost the 

 crusty layer (Woodcut fig. 7). The soft tissue between the crust and the fibre is here rather thin. The 

 fibre continues to the point of the papilla, where it ends at the outer end of the cavity there; it has an 

 average thickness of about i ram . The coating layer of the stalk and root is thin, and does not exceed 

 i mm in thickness. It is of a character somewhat different from what it is in the Asbesfophii>ia-s\><zc\zs, 



