156 HYALONEMA (HYALONEMA) OBTUSUM. 



As above stated the sponge-body was in life obviously attached to a bundle 

 of stalk-spicules, which have, however, been pulled out of it. Empty tubular 

 spaces, sometimes 0.9 mm. wide (Plate 36, fig. 26a), the walls of which are 

 formed by fine, highly stainable membranes, mark the places where the upper 

 ends of the largest of these stalk-spicules were situated. These spaces lie in the 

 axial part of the sponge-body. They are conical, attenuated above, and extend 

 upwards to within a distance of 2 mm. from the summit of the gastral cone. 

 In the lower part of the sponge-body these spaces are surrounded by a kind of 

 cement, composed of dense masses of stout, one- to five-rayed, most frequently 

 tetractine or diactine acanthophores (Plate 36, fig. 26). In this cement a 

 few microhexactine-derivate pachymicrohexactines also occur. Quite at the 

 bottom, a short distance below the dermal membrane, numerous slender-rayed 

 spicules with long spines, which I consider as slender acanthophores, form a 

 kind of felt. These spicules are mostly tetractines, but a good many triactines 

 and a few diactines, pentactines, and hexactines also occur among them. Transi- 

 tional forms, connecting these spicules on the one hand with the stout acantho- 

 phores above referred to, and on the other with the dermal pinules, are also found 

 in this part of the sponge. 



The thin marginal part of the circular wall which surrounds the gastral 

 cavity, and forms the boundary between the dermal and the gastral parts of the 

 surface, contains numerous, longitudinally situated, diactine pinules, the distal 

 rays of which protrude freely beyond the surface. 



The gastral surface, that is the surface of the gastral cone, and the inner 

 surface of the wall surrounding the fissure-like gastral cavity are covered with 

 micramphidiscs and gastral pinules. The micramphidiscs are situated irregu- 

 larly, and in some places are so numerous as to form dense masses. The gastral 

 micramphidisc-layer does not terminate at the openings of the efferent canal- 

 stems into the gastral cavity, but is continued in the walls of these canals and 

 their branches quite down into the innermost parts of the choanosome. The 

 gastral pinules are mostly pentactine, but hexactine forms also occur. Their 

 centres are 30-100 m apart. Their lateral rays extend paratangentially in the 

 gastral membrane; their distal apical rays arise vertically from the surface, and 

 protrude freely beyond it, forming a dense fur about 125 m high (Plate 35, figs. 1, 

 3, 16). This pinule-fur is not, like the micramphidisc-layer, continued down the 

 efferent canals, but terminates at their mouths. 



Small hypogastral pentactines, similar in position to the hypodermal pen- 

 tactines above referred to, occur below the surface of the cone. 



