PORIFERA. I. 



3^ 



papillse are more or less close-standing, always, however, rather close; they are slender and slightl\- 

 conical, decreasing in thickness npward, and the}' are unbranched or slighth branched. They may 

 otherwise be rather different with regard to length and thickness, and there nia>- be some difference 

 in individnal specimens. The papillse are stubb\- at the summit and apparently closed, or thcN- ma\ 

 be tapering and show an osculum. The colour (in spirit) is white and somewhat transparent, in some 

 .specimens with a slight yellowish red tint. In the middle of the transparent papillse is seen an opaque 

 whitish part. The consistency, especially in the lower part of the sponge, is rather firm. The surface 

 is smooth, without projecting spicules. The derma! mciiibraiif is thin and transparent, but rather solid, 

 and may easih- be torn off to some extent; it is provided with spicules forming in the upper part of 

 the sponge and especially in the papillae a beautiful reticulation of fibres. The reticulation may, with 

 regard to the width of the meshes, be somewhat different in different individuals. Towards the base 

 of the sponge the reticulation disappears most frequently, and passes into another arrangement of the 

 spicules, which are here lying close-packed in all directions in several layers, but parallel to the sur- 

 face. In the papillse the meshes are of the largest size, and here some of the fibres of the dermal 

 reticulation have a marked longitudinal direction. The porrs are found in the meshes of the dermal 

 reticulation, often so close as to reduce the membrane to a network. The sizes of the pores are 

 measured from o-o2 — o-i™'". They are chiefl\- found on the papillse, and here very close, but the\- are 

 also numerous on the other parts of the surface of the sponge, where nets of spicules are found in 

 the skin; on the other hand they are wanting or only found in very small numbers on the lower part 

 of the sponge where the spicules of the skin is close-packed. In the specimens examined they appeared 

 to be largest on the papillse, and to become smaller lower down, and the few pores found, where no 

 reticulation was present, were very small. Oscula are found in the ends of some of the papilUe; then 

 these papillse are conically tapering, and the spicules are here arranged parallel to the longitudinal 

 axis of the papilla and close together, and thus one of their ends is txirned towards the oscular 

 opening. 



The structure of the papilla'. The structure of the j^apilke of this species has never been 

 exacth- examined. Schmidt, however, mentions that they are hollow and thin-walled, and that a 

 fibre goes from the skeleton into each papilla, in which it radiates in an irregular wa}-. Fristedt 

 says that the inner structure is very characteristic, but does not enter into further details as to these 

 characteristic features. — The papillae are of two different kinds: pore papillae, and oscular papilla;. 

 Commonly they may already- be distinguished by their outer appearance; the pore papillae, at all events 

 their upper parts, are more slender and rounded at the top. Through their middle stretches a power- 

 ful fibre from the skeleton, from which pillars branch off to the network of the skin, supporting the 

 skin; the hollow of these papillse is a continuation of the subdermal cavities spread over the whole 

 surface, and the papillse are abundantl}- provided with pores leading into the hollow. The oscular 

 papillae most frequently are somewhat thicker than the pore papillae, and at the top the\- are, as has 

 been mentioned, conically tapering, and end here with an osculum; and in this tapering part the spi- 

 cules are lying close together parallel to each other and with one end turned towards the oscular 

 opening. The papilla is hollow and thin-walled; also here a fibre from the skeleton stretches up into 

 it, but this fibre runs along the wall, and most frequenth- it disappears in the uppermost part of the 



