in Octopus ventricosus the colour of the ink is pure black, and it is
blackish grey when diluted on paper. "The ink (_Edin. Phil. Journ._ vol.
xvi. p. 316.) brought in a solid state from China has the same pure
black colour as in the Octopus ventricosus, and differs entirely in its
shade, when diluted, from that of the Loligo sagittata, as may be seen
from specimens of these three colours on drawing paper. Swammerdam
suspected the China ink to be made from that of the Sepia; Cuvier found
it more like that of the Octopus and Loligo; but different kinds of that
substance are brought from China, probably made from different genera of
these animals, where they abound of gigantic size." At the present day,
according to Cuvier, an ink is prepared from the liquor of these animals
in Italy, which differs from the genuine China ink only in being a
little less black. (_Mem._, vol. i. p. 4.) Davy found it to be "a
carbonaceous substance mixed with gelatine;" but on a more careful
analysis, Signor Bizio procured from it a substance _sui generis_
[peculiar in kind], which he calls melania. "The melania is a tasteless,
black powder, insoluble in alcohol, ether, and water, while cold, but
soluble in hot water: the solution is black. Caustic alkalies form with
it a solution even in the cold, from which the mineral acids precipitate
it unchanged. It contains much azote: it dissolves in, and decomposes,
sulphuric acid: it easily kindles at the flame of a candle: it has been
found to succeed, as a pigment, in some respects better than China ink."
(_Edin. Phil. Journ._, vol. xiv. p. 376.)

[15] "The ink secreted in this bag has been said to be thrown out
to conceal the animal from its pursuers; but, in a future
lecture, I shall endeavour to show that this secretion is to
answer a purpose in the animal economy connected with the
functions of the intestines." (Hume's _Comp. Anat._ vol. i.
p. 376.) Dr. Coldstream, in a letter to the author, detailing