The different members of
this marine flotsam frequently rise and fall periodically: some of
them sinking by day to escape the light, others rising only by day;
others, again, appearing on the surface in spring, keeping deep down
in winter. Perhaps the majority of them are phosphorescent, sometimes
shining by their own light, sometimes borrowing a glory from
innumerable phosphorescent bacteria with which they are infested.
Nearly every class of the animal kingdom contributes members to this
strange population. The young forms of many fish, as for instance of
conger, flying gurnards, and some flatfish, are pelagic and have
colourless blood, and pale, transparent, gelatinous or cartilaginous
skeletons. The tadpole-like stages of the sea-squirts, which in adult
life are to be found attached to rocks like weeds, drift about in the
surface waters until their time comes for settling down in life. Many
other Ascidians pass their whole life as pelagic creatures. A few
molluscs, many kinds of worms, echinoderms, and their allies, crab and
lobster-like creatures in innumerable different stages of development,
are to be found there, while unnumbered polyps and jelly-fish are
always present. It would be difficult to imagine a better training for
the naturalist than to spend years, as Huxley did, working at this
varied assortment of living creatures.
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