FIG. 28.--Astacus fluviatilis.--A, a vertical section of the eye-stalk ( x 6); B, a small portion of the same, showing the visual apparatus more highly magnified; a, cornea; b, outer dark zone; c, outer white zone; d, middle dark zone; e, inner white zone; f, inner dark zone; cr, crystalline cones; g, optic ganglion; op, optic nerve; sp, striated spindles.
[Editor's note: illustration is reproduced here approximately twice the size of the woodcut in the book.]
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