matter belonging
to the whole colony. The lower portion of it is fixed in the muddy
bottom of the sea, but the upper portion is free, and gives off a
number of branches, on which the individual polyps are seated. The
whole colony thus has the appearance of a highly ornamental pen.

There is one British species, _Pennatula phosphorea_, which is found
in tolerably deep water, and is from two to four inches in length. The
specific name again indicates the phosphorescent quality belonging to
it. When irritated, it shines brilliantly, and the curious thing is
that the phosphorescence travels gradually on from polyp to polyp,
starting from the point at which the irritation is applied. If the
lower part of the stem is irritated, the phosphorescence passes
gradually upwards along each pair of branches in succession; but if
the top is irritated the phosphorescence will pass in the same way
downwards. When both top and bottom are irritated simultaneously two
luminous currents start at once, and, meeting in the middle, usually
become extinguished there; but on one occasion Panceri found that the
two crossed, and each completed its course independently of the other.
Those of our readers who have had opportunities of making or seeing
experiments with the sensitive plant (_Mimosa pudica_) will be
reminded of the way in which, when that plant is irritated, the
influence travels regularly on from pinnules to pinnules and pinnae to
pinnae.

In all the cases mentioned the phenomenon of phosphorescence is
exhibited by invertebrate animals; but though rare, it is not an
unknown phenomenon even in living vertebrates. In a genus of deep-sea
fishes called Stomias, Gunther mentions that a "series of
phosphorescent dots run along the lower side of the head, body, and
tail." Several other deep-sea fishes, locally phosphorescent, seem to
have been dredged up by the French ship Talisman in its exploring
cruise off the west coast of Northern Africa in 1883. During the same
expedition, a number of deep-sea phosphorescent crustaceans were
dredged up, the phosphorescence being in some cases diffused over the
whole body, in other cases localized to particular areas. In deep-sea
forms the phenomenon is, in fact, so common, as to have given rise to
the theory that in the depths of the ocean, where the light of the
sun cannot penetrate, the phosphorescence of various organisms diffuse
a light which limits the domain of absolute darkness.

So much by