The front of the eye-ball is
covered with a loose membrane instead of a cornea; the iris is
composed of a firm substance; and a process projects from the upper
margin of the pupil, which gives that membrane a semilunar form."[11]
The exterior coat or ball is remarkably strong, so as to seem almost
calcareous, and is, when taken out, of a brilliant pearl colour; it
is worn in some parts of Italy, and in the Grecian islands by way of
artificial pearl in necklaces.
[10] In all other worms the eyes are entirely wanting, or their
existence is very doubtful. Whether the black points at the
extremities of what Swammerdam calls the horns of the common
snail, are organs which really possess the power of vision,
is still problematical.
[11] Blumenbach, Man. Comp. Anat. p. 305.
Next we may notice the curious provision by which the Cuttle-fish is
enabled to elude the pursuit of its enemies in the "vasty deep." This
consists of a black, inky fluid, (erroneously supposed to be the
bile,) which is contained in a bag beneath the body.
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