the british - Corning Museum of Glass

xiv INTRODUCTION.
and stretching vertically through the cavity inclosed by
the column. Each principal septum (Plate XI. fig. 1, a),
in any of the normal species, is inserted, by its outer edge,
into the column-wall throughout its entire height; by its
lower edge, into the base, from the wall to the centre; by
its upper edge, into the disk, from the margin to the mouth;
and, by its inner edge, into the stomach, from the lip, almost
to the free bottom of that viscus. From thence the inner edge
recedes with an arching outline, and is free, until it is
gradually merged in the lower edge at the centre of the
base. Between these primary septa, others are developed
in succession, partitioning off the imperfect chambers thus
formed. But the septa of each successive cycle, while still
inserted in the column-wall throughout, spring from the
stomach at higher and higher points, and terminate at
points more and more remote from the centre of the base.
The number of septa depends, to a certain limit, on the age
of the individual, but in Peachia it never exceeds twelve,
and in Halcampa microps, eight.
In Peachia, the tissue of the septa is very dense, and
still more so in T. crassicornis, where it assumes a firmness
almost cartilaginous, and a decided blue colour.
The muscular tissue of the disk protrudes in the form
of hollow cones, which are the tentacles: each of these
springs from an interseptal chamber, and hence their development
is in cycles corresponding to that of the septa.
The fibres which compose their walls are very delicate.
3. Nervous and Sensory System. I have been as unsuccessful
as my predecessors, in my search for nervous threads
or ganglia; still, I have little doubt that such exist. I
should expect their presence in the form of a ring, surrounding
the mouth, perhaps with a pair of ganglia at the
gonidial tubercles, distributing threads to the tentacles.
I have never observed any trace of auditory vesicles or
otolithes, nor any organs that I could regard as eyes; not
even in the rudimentary form of those aggregations of pigment-cells,
that occur on the margin of the Naked-eyed
Medusæ. A delicate sense of touch certainly exists, distributed
over the entire surface, but specially localized in
the lips and the tentacles. The occasional elongation of
one or more of these latter organs, and their employment
(as described at pp. 34—36, infra), indicate the existence
of an active tactile faculty, and not merely of passive