18709. | Destructive Nature of the Boring Sponge. 281 
points. The mode of distribution and extension of the sponge 
would rather indicate that a process of chemical solution was the 
real agent at work in erosion. Of the exact constitution of this 
corrosive fluid we, however, as yet know nothing. The importance 
of the boring sponge in helping to effect the redistribution of 
eternal matter, does not consist in comminuting the stone into 
particles, but in dissolving it as sugar is dissolved in a glass of 
water, and mingled with the sea-water in this dissolved condition. 
Out of this solution the innumerable shell-fish take the mineral 
materials which have been mingled with their blood, and from 
which it is deposited as new layers on the shell, which, when the 
animal dies, either is also finally redissolved by the sponge, or 
falls to the bottom of the sea asa contribution to the earth’s 
strata of future zons.” 
Dr. Leidy? observes in regard to the agency of this organism in 
disintegrating the shells of dead mollusks, “ that an extensive bed 
of oysters, which had been planted by Thos. Beasley at Great 
- Egg harbor, and which was in excellent condition three years 
since (1857), had been subsequently destroyed by an accumula- 
tion of mud. The shells of the dead oysters, which were of 
large size and in great number, in the course of two years have 
been so completely riddled by the boring Cona, that they may 
be crushed with the utmost ease, whereas without the agency of 
this sponge the dead shells might have remained in their soft 
muddy bed devoid of sand and pebbles, undecomposed perhaps 
even fora century.” The ability of such an organism to comminute 
both organic and inorganic calcareous materials is well illustrated 
in the instance above cited, and their influence in modifying the 
character of marine deposits is clearly implied. 
n a specimen of the common Ostrea virginiana, recently 
handed me for examination by my friend, Mr. John Ford, the 
substance of the shell was thoroughly cavernated so as to render 
it extremely brittle and readily crushed; in fact the inner table 
of the shell left standing showed a great number of elevations 
within, which indicated points where the intruding parasite had 
been kept out by the: oyster which had deposited new layers of 
calcareous matter at these places so as to give rise to the eleva- 
tions spoken of. Besides this, the inner table had become so 
weakened at the insertion of the adductor muscles that the animal 
1 Proc. Acad. Nat, Sciences, Phila., VIII, 162. 
