Still further ancillary to the protection of the stomach from the
intrusion of inimical matters, we may safely suppose certain eye-like
specks which are placed at the very vestibule. In the larger species,
as this red-clouded green Squirter, there are seated in special
fissures at the very margin of the expanded siphon-orifices, red
dots,--eight around the receiving, six around the ejecting, siphon.
Each dot seems ascertained to be an eye of very rudimentary structure,
seated on a mass of orange pigment. We should probably do wrong if
we attributed any higher vision to these organs than a low degree of
sensibility to the general stimulus of the light.
Some species have the orifices of the siphons four-cornered, whereas
the sort I have been describing have them circular; there are
differences also in the breathing sac, which in the square-mouthed
species is folded lengthwise, while in the round-mouthed it is plain.
Hence the former have been separated from the _Ascidiæ_, as a distinct
genus, named _Cynthia_; both including a large number of species.
We have a pretty attractive little _Cynthia_ in our dredging,--the
Currant Squirter.[152] It is not uncommon in deep water off this coast,
and in Weymouth Bay; frequently occurring in family groups crowded
together on old shells. Generally there is one of superior dimensions
to the rest, the venerable parent of the colony; and, surrounding
him, others of varying size, and (doubtless) age, down to very minute
infants. The full size is about that of half a small cherry; but it
is more usual to see them not exceeding that of half a red currant.
These comparisons will also give a fair idea of their shape and
colour, especially in a state of contraction, as when lifted from
the water: for they are little hemispheres of a brilliant, scarcely
pellucid, crimson hue, seated on the shell by the whole broad base.
Under water, and at ease, the form becomes more conical, rising into a
point; whence, in full expansion, the two siphons protrude, slightly
divergent, and the one a little superior to the other, each opening by
a distinctly quadrangular orifice.