Wallich.^ on Siliceous Organisms. 
37 
information, inasmuch as I conceive tliat a large class of 
minute structures, and especially of Diatomacese, tlie exist- 
ence of which has hitherto been unrecognised, occur in the 
open sea, as strictly free-floating independent organisms ; and 
that extended inquiry will prove this class to be quite as 
numerous and interesting as any trith which we are already 
familiar. 
In another paper, on the Distribution and Habits of the 
Pelagic Diatomacese (a copy of which I shall have the honour 
of presenting to the Society in a few days), I have endeavoured 
to show that a vast number of these organisms are peculiar 
to the open sea, and that they possess a sufiicient degree of 
buoyancy to enable them to live and move amongst its waters 
without the aid of any supporting body whatever. I have 
also pointed out the causes upon which I consider this buoy- 
ancy depends, with my reasons for assuming that the move- 
ments of which these pelagic forms are in a special degree 
capable, and by means of which their bathymetrical range, 
under different circumstances, is determined, are entirely 
independent of the ordinary to-and-fro motile power shared 
by them, in greater or lesser degree, with all other free forms 
of Diatomacese. I should not, however, refer to this paper, 
were I not desirous of showing the important part performed 
by the Salpse in the accumulation of the deep-sea deposits ; 
and had not certain facts presented themselves, in connexion 
with the Salpse material generally, which tend to throw light 
on the occurrence of Xanthidia in the flints, and, if I mistake 
not, on the concretion of the flints themselves. 
On subjecting to pressure the small nucleus seen at one 
extremity of a Salpa, an ochreous-coloured pulpy mass 
escapes. Placed under the microscope, this is found to 
consist of a gelatinous -looking basis, throughout which are 
interspersed numerous minute granules, mostly of a yellowish 
hue, and consisting of particles of sarcodic and endochromic 
substance, extracted by the Salpa from the animal or vege- 
table structures upon which it subsists. The larger bodies 
mixed up with the gelatinous basis, consist chiefly of Diato- 
mace(B, Foraminifera, Polycystina, AcanthometrcR, spicules of 
Thalassicolla, Didyocha, and minute sponges, Xanthidia, oil- 
globules, and a host of doubtful objects, to which it would be 
difficult to assign either a name or a position. They all bear 
with them, however, unmistakeable evidence of having been 
taken from the waters around in a living condition, the soft 
parts of some being still intact, both as regards substance 
and colour ; whilst others present themselves more or less 
freed from their soft parts. In the case of the Diatomacese, 
