ANIMAL SENSE PERCEPTIONS. 331 



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,* the 

 mimicking resemblance of a Phasma to the leaf or twig on which 

 it was found would probably be much greater than that appre- 

 ciated 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. t 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 Verte- 

 brata, 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.' "| 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 v/ho had several times mistaken a " projecting corner of 

 a rough stone wall for a lady with flounced skirts " (' Edinburgh Review,' 

 January, 1895, p. 98). 



f Mr. Hickson has pointed out that in some fishes of the deep sea 

 (Scopelidce), " not being provided with well-developed eyes or phosphorescent 

 organs to attract their prey, the pectoral fins and the outer rays o"f 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. 



l ' Origin of Species,' 6th ed. p. 145. 



