jq6 PORIFERA. I. 



spicules project rather close to each other; the}' are stuck with one end between the parallel spicules 

 of the skin, while all the other part projects, so that the skin is very distinctly shaggy (PI. XIX, fig 3). 



Oscula and pores: In the examined specimens the pores were only found in small numbers; 

 they are small and difficult to observe, not going vertically through the dermal layer, and so their 

 outer opening is only little conspicuous when a piece of stained skin is viewed from above. The size 

 is measured from o-oii — o-oaS™". Oscula: as before said the surface has a larger or smaller number 

 of papillae, up to a score in the largest specimens. These papillae are formed by the dermal layer; the 

 spicules of the skiu are here arranged parallelly to the longitudinal axis of the papilla. On the summit 

 of the papilla the oscular opening is found; these openings, however, are not round, but are made 

 by the skin of the papilla being split into a number of narrow lobes, and according to this arrange- 

 ment the spicules in the outermost part of the papilla are gathered in a like number of bands (PI. XIX, 

 fig. 5). The papillae may have a somewhat different appearance, which would seem to be due to a 

 different degree of contraction. In their most extended form they are thin-skinned and translucent, of 

 a length of 6 — 7""°, are tapering and often compressed (PI. V, figs. 7 — 8). Then they may be shorter 

 and shorter, and at the same time they become round and more compact, and the end becomes stubby, 

 and assumes also a darker colour (PI. V, fig. 6). They may be so short as only to form a quite flat 

 prominence; at the same time a kind of folding must take place, for when such a papilla is viewed 

 from above under the microscope it is seen that the very close-packed spicules form, as it were, bands 

 or partition walls going from the middle towards the periphery (PI. XIX, fig. 6). 



The skeleton: As has been said above, the sponge is very cavernous, and therefore its body 

 consists mostly of more or less membrane-like parts which in the lower part of the sponge surround 

 and keep together an abundant mass of extraneous bodies, while in the upper part of the sponge they 

 surround and bound a number of cavities, into which the pores lead, and from some of which oscula 

 lead out. The skeleton therefore, besides of the mentioned dermal skeleton, consists of some irregular 

 fibres, partly found in the membrane-like parts separating the cavities, partly running freely here 

 and there, especially from the lower part to the dermal la\er. The fibres found in the membranes 

 are j^olyspicular , sometimes distinct and well defined, sometimes more dissolved in the membrane. 

 Besides with these fibres the membrane is also provided with diancistra hing in beautiful rosettes 

 rather close to each other (PI. XIX, fig. 4). Also the freely running fibres are polyspicular, and have 

 ratlier many spicula alongside. The thickness of the fibres is generally o-io— 0-17™"'. As in the pre- 

 ceding species diancistra are found in rosettes on the fibres. In the lower part of the sponge fibres 

 may be found where there is some interval between the incrusted extraneous bodies; where such is 

 not the case the parts of the tissue between the foreign particles are provided with diancistra placed 

 in rosettes in large numbers, and onlj' a few needles. Spongin is not seen in the skeleton. 



Spicula: a. Megasclera are styli; they are straight or slightly curved, sometimes a somewhat 

 sharper bend is found at the head end; they are thickest in the middle tapering somewhat to the 

 rounded end, though not so much as in the styli of the preceding species; the smaller needles are 

 least tapering, often quite imperceptibly, and sometimes not at all. The opposite end may be some- 

 what different; most frequently it has a very stubby point that may end in a quite small, pointed 

 process; in other cases the point is more long and evenly tapering. The length varies very consider- 



