276 
THE VOYAGE OF H.M.S. CHALLENGER. 
of ash after ignition, and this was almost entirely composed of silica. When living, 
or in the fresh condition, the relative amount of inorganic material would necessarily he a 
good deal smaller ; but the quantity of moisture normally present in the test cannot he 
estimated from specimens which have been preserved for a long period in alcohol. Under 
the microscope the appearance of the tubes is such as would lead to the idea that the 
chitinous or organic basis formed a much larger proportion of their entire weight. The 
arenaceous constituents consist partly of minute angular sand-grains embedded in the 
chitinous envelope but sufficiently exposed to impart a distinct roughness to the exterior, 
and partly of the empty siliceous tests of Radiolaria, which are present in considerable 
numbers in the mud of the sea-bottom at this particular locality. 
Boiling in water has no appreciable effect on the organism in the condition in which 
it has come into my hands, that is, after long maceration in alcohol ; and moderately 
strong acetic acid produces no perceptible change in it, even on the application of heat. 
Heated in dilute hydrochloric acid (one part of acid to four of water), there is at first 
a slight effervescence, the carbonic acid being evolved from a few minute Foraminifera 
built into the test rather than from any secreted calcareous matter, of which there appears 
to be little or none. After a time most of the tubes break up, and eventually become 
entirely disintegrated, owing apparently to the solution of the organic matter. In those 
which remain the test appears as a colourless sandy envelope, and the sarcode, which has 
swollen to its original size, as a granular, transparent, brown mass, filling the cavity of 
the tube, as shown in figs. 9, 10. 
With nitric acid (one part of acid to four of water), the disintegration is much more 
rapid, and after a time there is but little residue beyond the siliceous material originally 
embedded in the test. 
Treated with solution of caustic potash and heated, the tubes are considerably disin- 
tegrated, but in a different way. Those that have retained their form are split and 
empty, as though the contents had swollen to bursting before being dissolved out, as 
seen in fig. 11. Digestion was not carried far enough in these cases to affect the siliceous 
constituents, and what remains therefore is chiefly the inorganic portion of the invest- 
ment. 
At one of the localities in which RMzammina is plentiful there occurs in company 
with it an organism in some respects similar, but generally taking the form of little 
rosettes. It was at first thought that this also might belong to the Rhizopoda ; the 
more so, as some of the branches had. the appearance of subdivision into chambers ; 
further examination, however, has led to the belief that the structure is cellular, and that 
it pertains to the vegetable rather than to the animal kingdom. Fragments of Polyzoa 
and other similar organisms are often found entangled amongst the branches of 
Rhizammina when it is brought up in the weed-like masses already described. 
The Challenger Station alluded to, at which Rhizammina algceformis was so abundant. 
