PORIFERA. II. 



177 



mens are more flexible. The colour (in .spirit) is more or less dark brown, often quite black; a few- 

 pieces have kept their original lighter colour. The surface is smooth, without projecting spicules. The 

 dermal membrane is very distinct and may easily be removed. It is a thin and transparent film with 

 a special skeleton of dermal spicules lying horizontally in it, and it is supported by more or less 

 perpendicular pillars of dermal spicules. Pores and oscula: As mentioned above, pores are found on 

 one side and oscida on the other. On the pore side the spicules form a network, and the pores are 

 here very close-standing, especially in the grooves, while they are few or wanting on the walls sepa- 

 rating the grooves. Several pores are lying together in the meshes of the network, they are round or 

 oval and of a diameter from 0024 — o-i7 mm . On the opposite, more even side oscula are found, they are 

 present in large numbers and rather close-lying. They are circular or oval, their edge is most fre- 

 quently slightly rising, and generally somewhat fringed. Their size was measured from 2^5 down to 

 .cjmm The close-lying spicules of the skin reach into the fringes of the oscular edge. 



The skeleton. The dermal skeleton. A genuine dermal skeleton, lying in the membrane itself, 

 is found here, besides the skeleton that supports the membrane and also consists of dermal spicules. 

 The skeleton of the membrane itself is differently arranged on the two sides of the sponge. On the 

 pore side and especially in the grooves of this side a beautiful reticulation is found , recalling 

 the reticulation in Halichondria panicea. The reticulation is polyspicular and forms triangular or poly- 

 gonal meshes. It may have a somewhat different appearance, and the fibres may have more or fewer 

 spicules alongside, and also single spicules may be found subdividing the larger meshes by running 

 from the fibres in between the pores. Sometimes the dermal spicules form longer, thicker fibres 

 running irregularly, and the spaces bounded by these fibres are again subdivided by thinner fibres or 

 single spicules. On the walls between the grooves the reticulation may be more irregular, or the 

 spicules may be quite scattered. On the oscular side the spicules are not arranged in a network; they 

 are here scattered, or only gathered in a somewhat bundle-like way, and they are rather close-lying. 

 The dermal membrane thus equipped is on both sides of the sponge supported by pillars of dermal 

 spicules; these pillars issue from the skeleton below and pass to the dermal membrane, but they do not 

 pierce it. Generally the pillars spread a little in a penicillate way towards the ends. Most frequently 

 these pillars are short, only a little longer than one spicule, but under the grooves of the pore side they 

 may get a greater length. In these latter places large subdermal cavities are then formed, and the 

 cavities under the membrane seem upon the whole to be larger on the pore side than on the oscular 

 side. The main skeleton is a rather close, irregular, polyspicular reticulation; the meshes are triangular 

 or irregular, and no distinction can be made between primary fibres and secondary ones. The number 

 of spicules in the fibre may be varying, generally it seems to be two to six. In conformity to the 

 construction no longer fibres are found in the irregular net of meshes formed in this way. Sometimes, 

 however, longer fibres may be found, running chiefly in the longitudinal direction up through the 

 sponge, and especially to be seen in longitudinal sections parallel to the surfaces; but they are thin, 

 little conspicuous, and only- to be seen when sections of the skeleton are viewed under the microscope. 

 Down towards the base the sponge is most frequently rather hard and solid; the skeletal net is here 

 still more close than farther up, and the fibres are thicker and consist of more spicules; in other 

 respects, however, it has the same appearance as farther up, and has no longitudinal fibres; moreover, 



The Ingolf-Expedition. VI. 2. 23 







