I would add here one word on the true nature of the Millepores, long
misunderstood by naturalists, because it throws light not only on some
interesting facts respecting Coral Reefs, especially the ancient ones,
but also because it tells us something of the early inhabitants of the
globe, and shows us that a class of Radiates supposed to be missing in
that primitive creation had its representatives then as now. In the
diagram of the geological periods introduced in a previous article, I
have represented all the three classes of Radiates, Polyps, Acalephs,
and Echinoderms, as present on the first floor of our globe that was
inhabited at all. But it is only recently that positive proofs have been
found of the existence of Acalephs or Jelly-Fishes, as they are
called, at that early period. Their very name indicates their delicate
structure; and were there no remains preserved in the rocks of these
soft, transparent creatures, it would yet be no evidence that they did
not exist. Fragile as they are, however, they have left here and there
some faint record of themselves, and in the Museum at Carlsruhe, on a
slab from Solenhofen, I have seen a very perfect outline of one which
remains undescribed to this day. This, however, does not carry them
farther back than the Jurassic period, and it is only lately that I have
satisfied myself that they not only existed, but were among the most
numerous animals in the first representation of organic life.

The earliest Corals correspond in certain features of their structure to
the Millepores. They differ from them as all early animals differ from
the succeeding ones, every geological period having its special set of
representatives. But still they are always true to their class, and have
a certain general correspondence with animals of like kind that follow
them in later periods. In this sense the Millepores are in our epoch the
representatives of those early Corals called by naturalists Tabulata and
Rugosa,--distinguished from the Polyp Corals by the horizontal floors,