82 Mr. H. J. Carter on Grayella, Osculina, and Cliona. 



generally about the 18th, it was transferred to spirit and water 

 for preservation. 



Dec. 31, 1869. — On this day I picked up on the beach, after 

 a heavy gale from the south, among other living specimens of 

 sponges, two compact portions, rounded off by friction among 

 the shingle, each about 1^ inch long, not quite so broad, 

 and rather compressed, of a liglit yellow colour tinged with 

 red, and presenting a single large hole at one part. They 

 were portions of Halichondria suherea, Johnston (Brit. Spong. 

 p. 139, pi. 12. figs. 4-6); and on making a longitudinal section 

 of them respectively, each displayed the interior cavity of a 

 univalve shell, about an inch long, with the spire and colu- 

 mella complete ; only the whole was composed of sponge-sub- 

 stance, just as much as if it had been analogously lapidified 

 by fossilization. Indeed, to use a mineralogical term, the 

 sponge internally was a pseudomorph of the shell it had re- 

 placed. How the cavity of the shell had been maintained 

 during the transition can only be accounted for by the pre- 

 sence of a hermit-crab [Pagurus), which, although still in one 

 of the specimens, had quitted the other ; so that the Pagurus 

 must have been in the cavity of the shell all the time that it 

 was being replaced, particle after particle, by the sponge — a 

 process, however, which might have gone on very rapidly, 

 as infeiTed by Montagu {aj). Johnston, p. 140, I. c). 



This was not all ; for each sponge had enclosed at the 

 summit of the columella a little Murex (coraUinus?), about 

 four lines long, fresh in appearance, but empty, on which were 

 deposited, both inside and out, but chiefly between the costfe, 

 lines of spherical gemmules, of a yellow colour, and varying 

 from 4- to 8-830ths of an inch in diameter, which gemmules 

 were themselves already sunk to almost half their diameter 

 into the substance of the Murex. 



The gemmule was composed (when nearly dry, in which 

 state the specimens were examined) of a minutely dimpled, 

 amber-looking, soft, coriaceous envelope, lined by one more 

 delicate, colourless, and transparent, containing a number of 

 spherical cells about 1-1 660th of an inch in diameter — in 

 short, just like the gemmule or so-called seed-like body of 

 Spongilluj whose grouping (here exclusively round the little 

 Murex) they otherwise generally resembled. 



This at once decides the question of the possibility of cer- 

 tain sponges feeding on the organic matter of shell-substance, 

 just as certain Fungi feed on woody tissue. And in this in- 

 stance, we must regard this sponge {Halichondria sidterea), 

 from its habit, true pin-like spicule (that is, with a turban-like 

 head), compact structure, minute cancelli, and small, although 



