the british - Corning Museum of Glass

xii INTRODUCTION.
1. Tegumentary System. The skin is sufficiently distinct.
After a few hours' maceration in fresh water (Sag. bellis),
the epithelial and pigmental cells are easily removed with
a hair-pencil, leaving the outer layer of muscular fibre bare.
If the specimen be immersed in spirit for a day or two
(A. dianthus), the integument may be separated in flakes,
which, under the microscope, are seen to be composed of a
multitude of short corrugated fibrillæ, set in no definite
direction, interspersed with clear granules, pigment grains,
and cnidæ.
An examination of the living animal (dianthus, bellis,
crassicornis, Halc, chrysanthellum, Cor. viridis, &c.) shows
that the skin is composed of three elements, though these
cannot always be separated. A layer of epithelial ciliated
cells forms the first tunic: these are constantly in process
of being thrown off from the true skin, in the form of
mucus; but in some cases (Phellia,Edwardsia) they
entangle foreign matters, and retain their cohesion as an
investment more or less dense, and more or less firmly
adherent to the skin. Below this is the true skin, of a
more granular character, and carrying, imbedded in its
thickness, a multitude of cnidæ, whose discharging points
are directed outwards. Intimately connected with this
layer, but still lying sufficiently beneath it to be regarded
as a distinct stratum, are the pigment-cells, which impart
the colours to the animal.
The tentacles of Aiptasia and Anthea (less conspicuously
also of S. bellis) are lined with a dense layer of cells, forming
to the naked eye a dark brown lining. Some peculiarities
of these cells I have detailed (at page 167, infra): it is
probable that this layer may have some special function yet
unrecognised.
2. Muscular System. In most species the muscular framework
of the body is beautifully distinct, and the tissue is
readily isolable. The column is a cylinder of muscular
tissue, consisting of two layers, the outer composed of
transverse, the inner of longitudinal, fibres. The transverse
fibres are the more strongly marked: they average
about 0001 inch in diameter, and are never striate.
The cylinder which forms the column, is closed in most
species by two extremities, which are flat, like the top and
bottom of a tin canister: the former is the disk, the latter
the base. Each of these is but a continuation of the same