A monograph of the British fossil corals - kreidefossilien.de

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BRITISH FOSSIL CORALS.
septa, the pali, and the columella, is always closed at its bottom and open at its 'upper
extremity, where it usually presents the appearance of a sort of radiated cup, and constitutes
the calice. In some species, this central cavity, or visceral chamber, remains completely
pervious from one extremity of the corallum to the other ; and the membranous
appendices containing the reproductive organs, and situated in the loculi, extend to its
basis, without encountering any obstacle ; but in other species a certain number of transverse
irabiculce or si/napticulce extend from one septum to another at various heights, and
fill up, more or less completely, the inferior part of the loculi. In other cases, horizontal
or oblique laminae occupy the same position, and subdivide the loculi into a series of small,
irregular cells ; and sometimes these partitions are developed to such an extent that no
direct communication is preserved between the lower and the upper parts of the visceral
chamber, so that the calico, instead of resembling a deep tubular cup, is reduced to the
form of a shallow basin. In general, these transversal laminae, to which the name of
dissepiments has been given, grow from the sides of the septa in an irregular manner, and
do not unite so as to constitute complete horizontal tabulae, extending from wall to wall
but in some Corals, where the septal apparatus is even rudimentary, the bottom of the
visceral chamber is incessantly raised by the formation of new floors or tabula, which
extend horizontally through the centre of the Polypidom, and constitute, under the calices,
a vertical series of secondary chambers.
Intercostal dissepiments are frequently met with on the outside of the walls of the
corallum and in compound Polypidoms, where"- the costae are highly developed, a thick
cellular mass is
thus formed, and often assumes the appearance of a ctenenchyma, or common
tissue. In other instances, the calcified derm continues to extend exteriorly without constituting
distinct costal, and forms a dense or a reticulate tissue, which, in certain aggregate
Corals, is nowhere referable to any individual Polyp, and produces a sort of intermediate
mass or true ccenenchyma.
It is also to be remarked, that the exterior surface of most Corals is covered by a layer
of epithelic sclerenchyma, which is sometimes thick and spongy, but in general thin and
dense, and then constitutes a species of coating, which may be called the epilheca.
These different constitutive parts of the Polypidom furnish the principal characters
employed in the classification of Corals ; but the mode of multiphcation of the Polypi must
also be attended to in the methodical arrangement of these Zoophytes. In some species,
the young are only produced by the ova, and each corallum is formed by the skeleton of a
single individual ; but in most, reproduction also takes place by fissiparity or by gemmation,
and in those cases the young usually remain adherent to the body of then- parent, and
thus produce compound Polypidoms. The manner in which the different individual
Polypidoms, or corallites thus united, are grouped together, varies very much, and furnishes
also useful zoological characters. It is equally necessary not to neglect studying the
changes which take place in the structure of Polypidoms by the progress of age. Corals,
when young, are in general much less complicated than in the adult state, and the manner