Corals and coral islands.

34

CORALS AND CORAL ISLANDS.

out of a common spherical cell, as made out by Dr. Mobius in
his careful microscopic investigations. The Actinia affording
the results was the Urticina crassicornis, found in both European and American seas. The actual size of the cell represented in figure 6 is about a 5,000th of an inch. In fig. 7 the
lasso-cell has already taken form but is folded on itself; in 8,
there is a second infolding; 9 shows a return to a single fold,
and further progress in the forming cell; and 10, the straightened lasso-cell. Thus the work of replenishing, throughout
the body wherever lassos are used, is always going on.
The radiating partitions or septa in the internal cavity
of the polyp have along the outer free edge what looks like a
slender white cord attached to it by a much convoluted or
mesentery-like membrane; and this cord contains vast numbers of lasso-cells radiately arranged. These white cords
through the multiplied plaitings of the mesenteric membrane
have great length; and they sometimes extend up through the
stomach and pass out of the mouth; or they are extended in
loops through the walls wherever they may happen to be torn.
There are often also bunches of somewhat similar white cords
full of lasso-cells appended to the septa, which are extended
from the body through some natural orifices near the base of the
Actinia (especially those of the Sargartia family). Gosse calls
these cords Acontia. They extend out usually two or three
inches, and sometimes six inches, and thereby widen much the
stinging range of an Actinia, both for the purposes of defence
and attack.
Gosse, in his "British Sea-Anemones," gives the results of
some experiments with regard to the action of these lasso-cells
(cnidce), from which a few paragraphs may be here cited.
"It has long been known, that a very slight contact with
the tentacles of a polyp is sufficient to produce, in any minute