and the mimicking creature may possess the unison we see, but under different characters and under different conditions. Thus to a colour-blind person who visualizes blue as green, what we should understand as a wonderful resemblance in a blue animal to its blue environment would be to him the assimilation in colour of two green objects. To a near-sighted person,[1] the mimicking resemblance of a Phasma to the leaf or twig on which it was found would probably be much greater than that appreciated by the possessor of stronger and more penetrating powers of vision; and the same fact as observed by both would, if analytically recorded in each case, be capable of modifying or enlarging our conceptions of the phenomena or theory under consideration. But how much more cogent is this suggestion if we compare the resultant of human power of vision with that possessed by other animals—say, as low in the scale of derivation as insects—whose eyes have a structure so dissimilar to our own, and whose sensory impressions are therefore likely to be so totally diverse.[2] The very essence of the theory of evolution predicates a vast difference in the sensation of vision, which must vary as the organ does in structure. As Darwin observes:—"Within the highest division of the animal kingdom, namely, the Vertebrata, we can start from an eye so simple, that it consists, as in the Lancelet, of a little sack of transparent skin, furnished with a nerve, and lined with pigment, but destitute of any other apparatus. In fishes and reptiles, as Owen has remarked, 'the range of gradations of dioptric structures is very great.'"[3] Wal-
- ↑ Imperfect vision is a frequent cause of illusion. Prof. Sidgwick's Committee of the "Society for Psychical Research" were acquainted with a short-sighted friend who had several times mistaken a "projecting corner of a rough stone wall for a lady with flounced skirts" ('Edinburgh Review,' January, 1895, p. 98).
- ↑ Mr. Hickson has pointed out that in some fishes of the deep sea (Scopelidæ), "not being provided with well-developed eyes or phosphorescent organs to attract their prey, the pectoral fins and the outer rays of the pelvic fins have become elongated, and provided with special sense organs for searching for their food in the fine mud of the floor of the ocean" ('The Fauna of the Deep Sea,' p. 159).—There is a general similarity in the colouring of animals inhabiting these depths with the mud of the ocean floor, but "protective resemblance" can scarcely be claimed when the tactile sense compensates for the loss of sight.
- ↑ 'Origin of Species,' 6th ed. p. 145.
