356 A MONOGRAPH OF THE 



margined simple orifice ; at other times there is a central 

 conical elevation of the membrane with a very small orifice 

 at the apex, while in other cases the membrane is gathered 

 thickly and closely together in the centre of the area, so 

 that no orifice appears. When not occupied by an open 

 osculum the area assumes the appearance of a tense mem- 

 brane, and frequently has from one to five or six small pores 

 which are barely visible in the dry condition by the aid of 

 an inch lens, so that there is every reason to beheve that 

 in the live state it would be found that when not occupied 

 by an osculum, they were regularly furnished with pores. 



In a tuberous specimen from Mrs. Griffiths, about the 

 size and form of half a large cocoa-nut shell, each promi- 

 nence was terminated by one or more large open oscula, 

 which did not appear to be furnished with a membrane as 

 in the smaller and more regularly dispersed oscula. This 

 specimen is the only one in which I have observed such 

 large and expanded organs of this description. 



The interstitial spaces beneath the dermal areas are 

 sometimes very large, extending to nearly half an inch in 

 depth, and from three to four lines in breadth. Occa- 

 sionally they are divided into three or four secondary spaces 

 by membranous structm'e, but at other times they are com- 

 plete spaces, more or less abundantly lined with sarcode. 



The coriaceous structurg of the dermal areas is crowded 

 with spicula which frequently assume a fasciculated appear- 

 ance, but this is not the case with the interstitial mem- 

 branes of the mass, which vary considerably in the quan- 

 tity of spicula they contain, and they are always irregularly 

 dispersed through the structures. The whole of the mem- 

 branes are thickly covered with sarcode. 



I could not detect the dermal membranes separate from 

 the stout integuments of the surface; the whole of its sub- 

 stance is crowded with spicula irregularly mixed together. 

 The spicula of the skeleton and those of the dermis and 

 interstitial membranes are of nearly the same length and 

 form, the only essential difference is, that the diameter of 

 those of the former is much greater than that of the latter. 

 Their spinulation is exceedingly variable, passing from purely 



