PORIFERA. II. 129 



placed rather close together along the upper edge. In the above mentioned specimen which divides 

 above into four processes, three of these processes have each an oseulum, while the fourth one has 

 two oscula. Oscula are spout-shaped, a pointed, conical spout rising to a greater or smaller height 

 round the opening, which spout is formed by the dermal membrane; it is most frequently somewhat 

 twisted. In the membrane forming the spout dermal spicules are found, arranged parallelly to the 

 longitudinal axis of the spout, more or less gathered into fibres; these fibres arise from the fibres 

 supporting the dermal membrane, which continue into the membrane forming the spout. From the 

 oscular opening a rather wide canal continues far down in the sponge, running chiefly in the longi- 

 tudinal direction, but frequently irregularly curved. 



The skeleton. The dermal skeleton. The outermost branchings of the main skeleton towards the 

 surface are continued by short fibres of dermal spicules. The outermost spicula-bundles of these fibres 

 are spread in a penicillate or fan-shaped way, and they extend everywhere into the ridges between 

 the pore grooves, and project a little over the surface; horizontal spicules are not found, and the fibres 

 are arranged in such a way as only to be found in the ridges. In different places of the sponge these 

 fibres may be differently directed, perpendicular to the surface or more or less recumbent; thus they 

 are frequently directed towards the upper end of the sponge, and accordingly recumbent, when a piece 

 of the membrane is seen from above. The fibres formed by the dermal spicules are most frequently 

 about i mm long. The arrangement of the dermal skeleton reminds much of the structure in Artemisina 

 arcigera. The main skeleton is of dendritic type. From the base a few thick fibres rise, branching grad- 

 uallv up through the sponge, frequently coalescing and connected by more or less strong anastomoses 

 in different wavs, so that a chiefly dendritic, tolerably regular and rather densely branched skeleton 

 is formed. The outermost ramifications of the skeleton bend towards the surface at right or more or 

 less acute angles. Then these outermost ramifications of the skeleton, as mentioned above, continue 

 to the surface as fibres formed by dermal spicules. All the fibres are polyspicular, towards the base 

 they mav be very thick, up to o-5 mm , and they are here interwoven with a network of more or less 

 strong anastomoses. The outermost ramifications, just before the beginning of the dermal spicules, 

 have a thickness of ca. o-09 mm . Spougin is found in the fibres, which are, therefore, very solid, but the 

 spongin is white and clear, and so it is only to be observed with difficulty. In the lower part of the 

 sponge it coats the fibres entirely, but only with a very thin layer; farther up the spougin is more 

 scarce, and it is not seen in the dermal fibres. 



Spicula: a. Megasclcra. 1. The skeletal spicules are long oxea; they are slightly, rarely a 

 little more, curved; the curve is most frequently even, sometimes it is a sharper bend and localized in 

 the middle. The spicules are of about equal thickness throughout the length, and the point is middle- 

 long, frequently bounded by straight lines. The length is o-68— cr98 ram , most frequently nearer to the 

 latter limit than to the former; the thickness is 0-014— o-022 mm . A few developmental forms are seen, 

 all of which are long pointed. 2. The dermal spicules may be best described as tornota, but they 

 approach the form of oxea; they taper a little from the middle outward, the point may be somewhat 

 varying, but most frequently it is short. They are generally straight, sometimes a little curved. Their 

 length is 0-45— o-65 mra , their thickness ca. 0-007— o-on mm . Of this spicule very few developmental forms 

 were seen, and no quite young ones. But to judge, both from the quite equally formed ends of the 



The Ingolf-Expedition. VI. 2. 17 



