146 TnoiiECTA. 



fibres, and perpendicular to tliein, wliilst others give off a few branches. The 

 branched connecting-fibres are more prevalent towards the surface than in the 

 interior. The meshes are irregular, 0-7-1 millim. wide. In the stem the 

 network appears more uniform ; here the main fibres are 0*2 millim. thick 

 and only 0-5 millim. apart. The connecting-fibres are 0-04— 0*1 millim. thick, 

 and the meshes irregular, 0-4 millim. wide. 



The inhalant pores appear as circular or oval perforations, 0*07 millim. wide, 

 in the thin membranes, which are spread out in the round meshes of the 

 superficial cortical sand-net. "Wide canals lead down from them, perforating 

 the sand-cortex. These open directly into the large inhalant canal-stems, 

 which are 0-8 millim. wide, straight and cylindrical, and extend perpendicularly 

 from the surface down into the interior of the sponge. They are distally 

 joined by a few, not particularly wide, tangential canals. The inhalant branch 

 canals are often provided with annular constrictions ; their final ramifications 

 are about 0-09 millim. wide, twice as broad as the ciliated chambers. The 

 latter are spherical and sessile on the (0*04-0-06 millim. wide) exhalants, that is 

 to say there are no special efferent canals. The ciliated chambers are 0-045 

 millim. wide. The efferent pore is about half as wide as the chamber. The 

 exhalants join to form canals 2-3 millim. wide, in which membranes are 

 expanded, partially dividing them into series of compartments in open com- 

 munication with each other by large holes in the dividing membranes. 



In several specimens very regularly spherical bodies, measuring 0-5-2 millim., 

 were observed in the ground-substance ; these are composed of small round 

 cells, which appear to bud inwardly from the wall. Near the surface — the 

 margin in a section — these cells often stand in more or less regular radial 

 rows, thus indicating that they bud from the wall. The interior of this body 

 has not nearly so dense a structure as the wall. In it only scattered cells, 

 similar to those in the wall, are observed. The whole structure is surrounded 

 by an endothelial layer of flattened mesodermal c6lls. The round cells in these 

 bodies measure 0-01 millim. and are regularly spherical ; neither a nucleus nor 

 a cell-wall can be demonstrated in them when detached from the wall, and their 

 protoplasm is not affected by ordinary staining-fluids. Those cells which lie 

 close to the wall, however, and which appear to be younger than the detached 

 ones, are readily stained. I am rather inclined to regard this structure as a 

 parasite or commensal of a vegetable nature. It seems that the vital cells of 

 this parasitic organism are situated in the wall of the whole structure, and 

 rapidly produce spores, which bud from the wail and finally lie detached in the 

 interior. 



This structure may be similar to that described by Polejaeff * in his Caco- 

 ^pongia levis {Stelospongia australis). 



* N. de Polejaeff, Eeport on the Keratosa. — Reports on the Results of the Voyage of 

 II.M.S. ' Challenger,' vol. xi. part 24, p. 5G (1884). 



