20 Mr. H. J. Carter on the Anatomy 



the "pores" on the dermal surface to the ampullaceous sacs, 

 and the latter leading from the ampullaceous sacs in little 

 radicles, which uniting and interuniting at length form a large 

 canal that opens on the dermal surface in the "vent." 



Hence we shall have to examine each of these parts in 

 particular, and thus pass from the general to the minute struc- 

 ture of the sarcode, in doing which it will be advantageous to 

 divide the latter into that of the surface and that of the in- 

 terior — the former under the term of " dermis," and the latter 

 under that of the " body." 



Dermis. 



The dermal surface of sponges varies with the species : it 

 may be uniformly smooth, or uniformly irregular, or uniformly 

 hispid, aculeated, and even prickly, soft or hard ; while in 

 composition it may be sarcodic, horny, spiculous, or sabellous ; 

 but the chief points to remember are that the dermal sarcode 

 or cuticle is supported for the most part by a subjacent reticular 

 structure or framework, composed of one or more of these con- 

 stituents, in the interstices of which the pores are situated, and 

 here and there the vents, scattered singly or in groups. 



This reticular framework when soft is formed of anasto- 

 mosing fibre composed of elongated, spindle-shaped, granuli- 

 ferous, nucleated, gelatinous cells, which lie parallel to each 

 other (the " muscular cells " to which I have alluded, and 

 which will be more particularly described hereafter) — or of 

 simple horny fibre — or of horny fibre with a core of foreign 

 bodies (the so-called arenaceous fibre) — or of horny fibre with 

 a core of " proper spicules " (spiculo-horny fibre) — or of fibre 

 composed almost of proper spicules alone (spiculo-fibre) — or 

 of arenaceous fibre bearing foreign bodies on its outer surface 

 as well as internally — or of spiculo-horny fibre or spiculo- 

 fibre bearing respectively tufts of proper spicules on its external 

 surface, so as to present a hirsute appearance, or with the same 

 tufts so enlarged as to come into contact and thus to form a 

 continuous incrustation ; or, indeed, there may be no fibre at 

 all but a smooth membraniform envelope composed of horny 

 sarcode imbedding spicules of the species horizontally placed 

 with respect to each other like a textile fabric, as on many of 

 the deep-sea sponges dredged up on board H.M.S. ' Porcu- 

 pine,' but always leaving apertures for the pores and vents 

 respectively. 



The " reticular framework," again, is supported on, if not 

 given off from, the dermal extremities of the main or vertical 

 lines of fibre of the skeleton, which may terminate at once on a 



