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change ; but when there comes to be a specially sensitive spot, 
anything which casts a shadow on that spot alone, produces 
an internal change. And as that which obscures only a small 
part of the organism is usually a comparatively small object, 
this advance from diffused sensitiveness to concentrated 
sensitiveness enables the organism to respond, not only to 
marked general changes in luminousness which its environ- 
ment undergoes, but also to marked special changes in 
luminousness caused by the motions of adjacent bodies.'’^* 
Mr. Spencer here commences to travel from the sensation 
of the oyster to the perception of the eagle. This is there- 
fore an important turning-point, being nothing less than a 
line of higher departure. We can see how he shows that the 
sensation caused by actual contact, which all organised bodies 
manifest, might, by the known action of light upon a sensitive 
organism, set up a higher degree of nervous activity in that 
part of the organism which was thus acted upon ; which 
higher nervous activity would, in accordance with well-known 
physiological laws, slowly but surely produce such structural 
modification as would enable the organism to detect the 
existence of opaque bodies not in actual contact with it. The 
remarkable fish, the Scop ulus, which inhabits the lowest 
depths of the Atlantic, and hence needs more light, to obtain 
which light it has developed three imperfect eyes on each side 
of the back, is perhaps a concrete example illustrating Mr. 
Spencer^s abstract statement. It is quite certain that if our 
sense of touch were made fine enough it could appreciate the 
impact of beams of light. Professor Crookeses beautiful ex- 
periments, showing the dynamical power of light, sufficiently 
prove this. The transition, therefore, from sensation to per- 
ception is not intrinsically improbable. But let this be dis- 
tinctly remarked. Whatever increase of Mind or of nervous 
sentiency we attribute to a creature thus developed, to that 
increase Mr. Spencer has no manner of right. He must steal 
every particle thereof. If the Mind in the nervous organisa- 
tion of a creature able to detect only actual contact be 20, 
and the Mind in a creature able to detect an object not actually 
touching it be 25, that difference of five represents so much 
Mind that the exigencies of Mr. Spencer’s argument compel him 
to purloin. As nervous matter is specialised and differentiated 
it needs Mind as, so to speak, its subjective lining; and as 
Mr. Spencer has never shown how he can honestly obtain one 
particle of this fining, we have no choice but to declare, since 
* Principles of Psychology, second edition, vol. i. p. 314. 
