356 DR. nowERCANK oi^ ALCvoNCELLUM spficTosUM. [Mar. 28, 



ridge is coeval with a very early condition of the animal, and that 

 the increment of the sponge has taken place in the space existing 

 hetween its base and apex. In the type specimen formerly in the 

 collection of the late Mr. Cuming, a few ridges such as occur on its 

 outer surface were apparent on its inner one, a little below the os- 

 cular area ; but I have not detected them in the corresponding situ- 

 ation in the specimens in my own possession. 



The oscular area within its beautiful circular frill or ridge is en- 

 tirely filled with oscular orifices. The network of which it is formed 

 is simple and irregular in its structure ; the rete is composed of nu- 

 merous closely compacted fibres, so arranged as to afford the greatest 

 amount of resistance in the least possible space, A transverse section 

 of one of these fibres would be like that of a douI)le convex lens. 

 The excurrent orifice of this great terminal network is well indicated 

 by the absence of interstitial spicula within its area, although on the 

 inner surface of the oscular ridge bounding it they are in as great 

 abundance as on other parts of the body of the sponge. In the 

 living condition there is little doubt that the whole of tlie area would 

 be furnished with a stout dermal membrane containing the true 

 oscula of the sponge. In one of the areas of the- oscular network of 

 one of my specimens, near its margin, I found a fragment of such a 

 membrane, about an eighth of an inch in diameter, in a fine state of 

 preservation. It was furnished with a reticulation formed of nume- 

 rous long acerate spicula closely fasciculated together ; and in con- 

 junction with this network there was a layer of sarcodous membrane, 

 in which several of the well-known forms of the interstitial spicula 

 of the sponge were imbedded, thus verifying the reticulated struc- 

 ture as a portion of the tissues of Alcyoncelliim ; but the semi- 

 detached state of the fragment forbids our assigning it with certainty 

 to the dermal tissues of the sponge. The sarcode is abundant on 

 this fragment ; and, as in other smaller fragments of that substance 

 which 1 have found adhering to parts of the skeleton, the colour is 

 that of a full amber-yellow. 



The series of equidistant circular apertures disposed in single lines 

 between the primary lines of the skeleton are evidently the inhalant 

 areas of the sponge ; and above eacli of these in the living condition 

 there is most probably a congregation of pores, like those above the 

 intramarginal cavities in Geodia and Fachymatisma. The margins 

 of these apertures consist of a stout ring of siliceous fibres, very like 

 those at the summits of the diagonal ridges on the body of the 

 sponge. 



The interstitial spicula of this sponge afford a numerous and beau- 

 tiful series of objects for the microscopist ; and some of them appear 

 to be peculiar to this species. In well-preserved specimens of the 

 sponge that have not been washed and bleached to make them look 

 ])retty, they are so numerous and so closely jjacked together that in 

 some parts they entirely obscure the view of the skeleton-lines be- 

 neath them ; and, if we may judge by analogy, their ofl^ice is to aflPord 

 points of adhesion to the interstitial membrane, and thus to vastly 

 increase the amount of surface of the nutrient membranes and sar- 



