THE COMMON SPONGE. 3R9 
Halichondria celata establishes itself in the small holes which 
some of the smaller annelides drill in the shell of the oyster, 
eat further and further into the unfortunate molluse’s vitals, 
causing the softer parts of the shell to rot away, and spread 
through its whole substance, like the dry-rot fungus through a 
solid beam of timber, until, sinking under the weight of his 
misery, the poor victim perishes, and his loosened shell is ca t to 
the mercy of the waves. On the other hand, some marine Acorn- 
shells nestle habitually in a sponge, the normal construction of 
the base of the shell being altered to suit the peculiarities of its 
habitation, so that in this instance, as in many others, there is a 
foreseen relation between two very dissimilar animals. Amongst 
the reticulated fibres of its spongy dwelling, the Acorn-shell 
finds a secure refuge in its infant state, and is soon enclosed by 
the growing fabric of the sponge-animal, except a small opening, 
which is kept clear by the vortex occasioned by the constant 
motion of its feelers or tentacula. 
But very few of the manifold species of sponges are of any use 
to man. The common sponge of commerce (Spongia communis), 
so serviceable in our households, is most abundant in the Lycian 
seas, where it is found attached to rocks at various depths 
between three fathoms and thirty. When alive, it is of a 
dull bluish black above, and dirty white beneath. There are 
several qualities, possibly indicating as many distinct species. 
“The most valued kinds,” says Edward Forbes, “are sought 
for about the Gulf of Macri, along the Carian coast, and round 
the opposite islands. The species which live immediately along 
the shore near the water’s edge, though often large, are worthless: 
These are of many colours; some of the brightest scarlet or 
clear yellow form a crust over the faces of submarine rocks ; 
others are large and tubular, resembling holothurize in form 
and of a gamboge colour, which soon turns to dirty brown when 
taken out of the weter; others are again lobed or palmate, 
studded with prickly points, and perforated at intervals with 
oscula. These grow to a considerable size, but, like the former, 
are useless, since their substance is full of needles of flint.” 
Large quantities of excellent sponge (Spongia usitatissima) 
are likewise imported from the West Indies. 
