4 Mr. H. J. Carter on three Pachytragous Sponges 



tough, resistant. Surface undulating, smooth, soot- or bottle- 

 black, shining, puckered towards projecting points of the rock 

 beneath. Dermal layer (figs. 1 a, 2 a) thin, colourless, transpa- 

 rent, rugose, charged with minute bacillar spinous spicules ; 

 presenting here and there large exhalant apertures (oscules), 

 singly or in groups, with raised margin, crateriform, also mi- 

 nute inhalant apertures (pores) generally all over the surface 

 of the sponge, amidst the projecting points of the large spicules 

 of the interior, and numerous circular, papillary eminences of 

 a lighter colour, caused by the projection of certain cells (be- 

 yond others) of the subjacent celluliferous layer. Celluliferous 

 layer {h) cortical, thick, continuous all round the sponge, and 

 often for a short distance into the mouths of the larger oscules, 

 much thicker on the free surface than at any other part ; co- 

 vered by the dermal layer above, in contact with the next or 

 spiculiferous layer internally ; composed of cells imbedded in 

 a kind of sarcodal trama ; cell (fig. 6) globular or oval, con- 

 sisting of a cell-wall in which is contained a large transparent 

 nuclear (?) body (o) and a small nucleolar (?) one (6), together 

 with a great number of free cellules (c), in each of which is 

 one or more black granules {d) , the black granules collectively 

 giving a black colour to the cell, and an intense black colour 

 to the layer composed of them (fig. 1 h) . Spiculiferous layer 

 (fig. 2 c) thin, composed of the large trifid spicules of the 

 sponge densely packed together ; in contact with the celluli- 

 ferous layer externally, and with the body-substance of the 

 sponge internally. Body-substance (figs* 1 c, 2d) composed of 

 more or less areolar sarcode, which is in direct connexion with 

 the pores, and traversed by the branches of the excretory 

 canal-system, which, uniting together, finally terminate in 

 their respective oscules ; charged more or less with the spi- 

 cules about to be described, and a great number of the black 

 cells (fig. 3 c), which thus give it a dark tint, although always 

 much lighter than that of the black cortical celluliferous layer. 

 Spicules of three kinds: — 1, trifid (fig. 3), large, stout, consisting 

 of a straight, smooth, pointed shaft and three expanded arms, 

 so much like a quadriradiate spicule, from the rays being so 

 much like each other, that, but for the shaft being a little 

 longer and straight, while the arms are slightly flexuous, the 

 diflference would be inappreciable ; 2, minute baciUiform or 

 fusiform spicide (figs. 3 a, 4), covered with spines, which are 

 vertical in the centre, but become more inclined towards the 

 extremities of the shaft ; 3, minute tricurvate or bow-shaped 

 spicule (figs. 3 J, 5), of hair-like thinness and equal in size 

 throughout, except at the ends, which are slightly pointed 

 and slightly turned up. The large trifid spicules are scattered 



