PORIFERA. I. 33 



papilla. If the wall is examined, it is found to be abundantly provided with pores, and so it would 

 be an obvious conclusion that these pores are leading directly into the oscular canal. A closer exami- 

 nation shows, however, that the oscular papilla is double-walled, or, in other terms, that the subdermal 

 cavities continue over the oscular papillse. These subdermal cavities are oftenest narrow, so that the 

 wall without any closer examination may convey the impression of being single. Where the fibre 

 passes into the oscular papilla the subdermal cavities are somewhat wider, and the fibre runs in the 

 partition-wall between the oscular canal and the subdermal cavit}-, so that in a transverse section the 

 large oscular canal is seen with some smaller cavities around it, which are subdermal cavities; some- 

 times these cavities are so large, that it cannot be seen immediately in the section, which of the cavi- 

 ties is the oscular canal; generally, however, the oscular canal is seen in the transverse section to be 

 lying at one side and the subdermal cavities at the other, and to be arranged in such a way, that the 

 outer wall and the partition-wall form two excentric rings, one within the other (PI. X, fig. lo). The 

 partition-wall is a tliiu, transparent membrane, not as the dermal membrane provided with a network, 

 but supported by branches that from the fibre bend regularly into it; besides a few spicules are found 

 spread in it. I have not been able to decide with certainty, whether the oscular papilla is always 

 double-walled through its whole extent, that is to say, whether the subdermal cavities stretch quite 

 round the oscular papilla, and perhaps some difference may be found in different papillae with regard 

 to this feature; if they go quite round, they are at all events most frequently very narrow on the side 

 of the papilla opposite to the fibre. Besides the structure as here described, which is the plainest 

 form, complications may occur; thus the pore-papilla and the oscular papilla may be united into one 

 papilla, so that one osculum or a couple of oscula may be found more or less far down the side of 

 the pore papilla; this fact alters nothing in the inner structure of the papilla, and otherwise the relation 

 between the oscular canal and the subdermal cavities may be somewhat varying. It would seem that 

 more or less complete partition-walls may also be found in the pore papillae, and finally the possibility 

 is not excluded that in many of the papillae appearing as pore papillae, an excurrent canal may be 

 found, although for the present there is no visible or functionating osculum. 



The skclftoiL. Besides the dermal skeleton and the skeleton of the papillae mentioned above, 

 the other skeleton of the sponge consists of some loose fibres and between these numerous and rather 

 close-set spicules, lying in every direction without any order; the fibres have a somewhat irregular 

 course, but chiefly they run from the base towards the surface; all the larger canals have the same 

 direction. The fibres may in some places be closer than in others, and be gathered almost as bundles; 

 they are rather thin, their thickness not exceeding o-og™'", while the fibres of the papilla: may have a 

 thickness of up to 1-5""". 



Spicula are oxea; they are very long tapering, almost from the very middle, and most frequently 

 thev are slightlv curved; the curve may be even, but is often a more or less sharp bend in the middle, 

 .so that the spicules are quite like those of Halkhondria panicea, but the\- reach a considerably greater 

 length than is common in this species. The length varies from ca. 0-36— o-S""", the thickness, which 

 is not always largest in the longest spicules, varies from o-oii — o'OiS""". Otherwise the size may vary 

 somewhat in different individuals; thus in one of the specimens in hand (the largest one) the spicules 

 reach a length of up to i-oj""", and a largest thickness of 0-02™"'. Shorter and finer, to quite fine 



The Ingolt-Expedilion. \"I. i. 5 



