PHYLL08PONQIA. 119 



exhalant canals. The latter lead into the loose and lacunose tissue which 

 occupies the grooves below the aconulous membranes. There are constric- 

 tions at the openings of the exhalant canals into these lacunas. Appa- 

 rently sphincters are situated here, which regulate the water-current. The 

 grooves are traversed by fine membranes, perforated by large holes connecting 

 the different cavities. All the lacunae in the different parts of the sponge com- 

 municate with each other ; and in particular it is important to note that the 

 lacanre in the grooves on both sides of the lamellar sponge are in com- 

 munication, by means of large oblique canals perforating the sponge and leading 

 from the grooves of the outer surface to those of the inner. These lacunre 

 finally open out into the oscula. There is no difference in the structure of the 

 lacuns& in the grooves of the two sides. 



The sJceUton consists of a network of fibres in the interior and a dense sand- 

 cortex on the surface. The former — the stipporting-sTceleton — is composed of 

 main fibres 0"18 millim. thick, which radiate from the peduncle and extend to 

 the margin of the lamella or cup. There is only a single layer of these fibres 

 in the sponge, which occupies the centre of the lamella. The main fibres are 

 continuously branched, the branches extend radially like the stems ; they 

 have an uneven surface, and are charged with large axially situated sand-grains, 

 which lie so close together that they form a continuous column. Although 

 these primary main fibres bend irregularly, they always extend, on the whole, 

 radially. From these fibres, which constitute the main support of the sponge, 

 branches are given off which curve towards the surfaces of the lamellce and 

 ramify in a penicillate manner. All the branches are curved so as to abut per- 

 pendicularly on the surface. They are, on an average, 0-12 millim. thick ; 

 stand pretty close together in the projecting conulous portions of the sponge, 

 but are absent in the lacunose tissue of the grooves ; they are similar to the 

 central fibres above described, and like them contain an axially situated column 

 of foreign bodies. Between these main fibres a network of connecting-fibres, 

 0-025-0-06 millim. thick, extends. These are entirely free from foreign 

 bodies of any kind. They are branched and form a true network, the meshes 

 of which are, on an average, 0*2 millim. wide and of varying shape. Also 

 these connecting-fibres are principally found in the more solid conuliferous 

 portion of the sponge and in the centre. Exceptionally, however, they extend 

 also for some distance into the fine membranes, which are expanded in the 

 lacunose tissue of the grooves. Such fibres are, however, very much thinner 

 than the ordinary connecting-fibres, measuring only 0*01 millim. in thickness. 



Geoqeapkical Disteibution. — Otaheite (£^ZZ^s) ; Zanzibar (T/yaW); Glorioso 

 Islands (' Alert ') ; Seychelle Islands (' Alert ') ; Amiraute Islands (• Alert ') ; 

 Admiralty Islands ; off Wild Island (' Challenger ') : Philippines (British 

 Museum) ; Moluccas (Wallace). 



