418 REVISION OF THE MONAXONID SPONGES, ill., 



short stalks, each about 5 mm. in diameter, and each with its own 

 "head" of branches, arise independently. The stoutest branches 

 are 4 to 5 mm. in diameter ; the slenderest, about 2 mm. 



The skeleton, as seen in section, presents quite different aspects 

 according- as the mounting- medium is balsam or glycerin. In the 

 latter medium, the spicules being thereby rendered almost indis- 

 cernible, it appears as if mainly consisting of a small meshed 

 irregular reticulation of colourless, or (in older parts of the 

 sponge) faintly yellowish-tinted, spongin fibres, of diameter sel- 

 dom exceeding 50 or 60/x; the reticulation, which is not more con- 

 densed in the axial than in the peripheral region of the branches, 

 and in pattern bears a certain slight resemblance to that of the 

 skeleton of Euspongia, is formed by longitudinal main fibres pau- 

 ciserially cored by principal spicules and by a network of connect- 

 ing fibres which are without contained spicules. 



On the other hand, in sections mounted in balsam, the spongin 

 fibres are difficult to perceive, and may even be quite invisible; 

 and the skeleton then shows itself as a lattice-like interlacement of 

 longitudinally-running (or, if near to the surface, slightly out- 

 wardly-trending), mostly paucispicular, loose strands of principal 

 spicules, interspersed between which, in comparatively small num- 

 ber, are single spicules likewise with a generally longitudinal orien- 

 tation. In addition, isolated single spicules constantly occur, which 

 are disposed transversely to the prevailing direction, and are con- 

 sequently very noticeable even although comparatively few. The 

 interlacing spicule-strands are constituted partly by the spicules 

 which core the main spongin-fibres and partly by spicules which 

 lie extra-fibrally ; some of the latter are directed with their apex 

 pointing to the contrary direction, i.e., towards the base of the 

 sponge Echinating acanthostyli occur only sparsely and irregu- 

 larly upon the fibres of the interior; and since (in balsam) the 

 fibres themselves are not readily perceived, these acanthostyli 

 appear at first sight as if scattered. On the other hand, in connec- 

 tion with the superficial fibres (comprising not only those situated 

 most externally, i.e., in immediate juxtaposition to the dermal 

 layer, but usually also most of the longitudinal fibres running near 



