98 THE VOYAGE OF H.M.S. CHALLENGEE. 



with certainty determine, since I was never able to find a completely intact graphio- 

 hexaster. I am, however, inclined to the former opinion, since I have always found a 

 number of these rhaphide bundles together, and in the neighbourhood usually a small six- 

 rayed cross, with a discoid expansion of the cylindrical principal rays, from which numerous 

 small points projected like the broken ends of fine terminal rays. The whole exactly 

 resembled the middle portion of a graphiohexaster whose terminal rays had been broken off. 



The sword-like hexacts of the dermal skeleton are distinguished by the strength of 

 the four tangential and of the distal rays, all of which terminate in rounded off extremities, 

 while the j^rolonged proximal gradually decreases in diameter towards the extremity, 

 and finally terminates in a conical point. The distal ray corresponding to the hilt of the 

 sword bears, sometimes in the middle or towards the outer extremity, a club-like 

 thickening (PI. XI. fig. 6). 



On the distal ray of most of the hypodermalia a fioricome occurs, which is distinguished 

 from those of Euplectella aspergillum by the greater number (fifteen) of the S-like 

 curved terminal rays on each principal, and by the wider cup-like form of each whorl of 

 terminals (PI. X. fig. 2). 



A special gastral skeleton is always absent where the large beams of the lattice-work 

 directly form the inner wall. Where this is not the case, it consists of simple hypogastral 

 pentaets, with four equally long intersecting rays, lying on the parenchymal side of the 

 gastral membrane, while the prolonged unpaired fifth ray penetrates widely into the 

 parenchyma (PI. XL fig. 2). 



The extremities of all the five rays are simply rounded or slightly knobbed ajid 

 thickened, only the prolonged distal is sometimes narrowed towards the extremity, 

 and may even terminate in a point. 



I have named this memorable sponge in honour of my esteemed friend and colleague 

 Professor Walter Flemming of Kiel. 



Since the single and much damaged specimen of Walteria flcmmingii is inhabited 

 by many comparatively large commensal hydroid polypes, which have doubtless pro- 

 duced the peculiar tubules running obliquely or at right angles to the peripheral strands 

 (PI. X. figs. 4, 6 ; PL XL fig. 4), the question arises whether we have here to do with a 

 normally formed individual, or not rather with one essentially modified. In specimens 

 without these invading polypes, the wide lumen of the parietal gaps may be in 

 great part filled up by the soft portion of the body-wall, which is here restricted almost 

 exclusively to a cortical layer for the supporting beams. 



I know of at least one case in another group of sponges, namely, that of a 

 Myxilla, found abundantly near Trieste, which is normally a compact bulbous body, but 

 which when invaded by Stephoscyphus mirabilis becomes bush-like, resembling a tuft 

 of the common heath Calluna vulgaris. 



