204 THE VOYAGE OF H.M.S. CHALLENGER. 



examination, though perhaps iu a less satisfactory state of preservation, I will add 

 to the above account some supplementary details. 



The smooth cake-like specimen figured by Wyville Thomson (figs. 5, 6) was 

 not when I received it so weU preserved as it appears in the woodcuts referred to. 

 The specimen is represented in PI. XXIX. figs. 2, 3, of the natural size, after a photograph 

 from either side. It is evident that half the fringed margin (from which a rectangular 

 portion has been cut for investigation) is well preserved, while the rest of the 

 marginal portion seems compressed and torn. The side represented in fig. 3, covered 

 with a somewhat wide-meshed network of more or less thin strands, exhibits a tolerably 

 uninjured surface, and is almost smooth with the exception of the projecting knobs about 

 the centre of the (uninjured) disc. On the other side, however (fig. 2) the marginal portion 

 exhibits for about a finger's breadth an intact dermal layer, with a fine-meshed lattice- 

 work, through which were seen the large deep apertures or pits of the parenchyma, 

 occurring at uniform distances of about 5 to 8 mm., as figured in the woodcut (fig. 5) 

 of WyviUe Thomson's Atlantic. The middle portion of the flat sponge body is on the 

 same side much injured and apparently compressed (PL XXIX. fig. 2). 



From Wyville Thomson's account this latter somewhat inbent side (PL XXIX. 

 fig. 2 of my figures, and fig. 5) is said to be the upper, while that covered by the 

 wide-meshed sieve-net and bearing a projecting central boss be the lower (PL XXTX. 

 fig. 3, and fig. 6). The projecting central protuberance of the latter is, according 

 to Wyville Thomson, the narrowed basal portion, from which the long tuft of needles 

 was torn away. 



The results of my investigation force me, however, to another conclusion, namely, 

 that the side covered with the wide-meshed sieve-network is the upper, while the other 

 with the fine superficial lattice-work and the subjacent pits of the parenchyma is the 

 lower or outer. This is proved first of all by the character of the superficial layers. 

 The wide-meshed framework which covers the surface (fig. 3) exactly resembles 

 the sieve-plate present in the funnel-shaped second specimen (PL XXIX. fig. 1) of the 

 same species, while the fine-meshed dermal layer which covers the undamaged marginal 

 zone on the other side (PL XXIX. fig. 2) corresponds exactly iu structure to the dermal 

 membrane of all Hexactinellids and especially to that of the funnel-shaped specimen 

 (PL XXIX. fig. 1) of the same species. 



The boss-like elevation iu the centre of the surface furnished with the wide-meshed 

 network does not represent the narrowed basal end of the body, but the conus centralis 

 which occurs on aU species of Hyalonema. The narrowed basal end of the sponge body 

 has, on the other hand, been torn off with the basal tuft of spicules, and is therefore not 

 to be seen on the lower surface of the body (PL XXIX. fig. 2). We have here apparently 

 a specimen of Hyalonema toxeres, which, after the tearing away of the basal tuft and 

 lower end, has been forced by oblique pressure into a flat compressed form. The normal 



