It is evident that the effect upon the hen must be greater in proportion as the sex marks and species marks of the male are more clearly defined, and therefore easier to perceive. Not only as means of recognition, but also as instruments for sexual incitement, colour-patterns with lucent points must be more advantageous than any other system of decoration. It is easily understood that a design like that on the tails of pheasants and peacocks is eminently capable of attracting the female attention to the displaying cock. But it would be stretching the theory too far if the marvellous “balls on sockets” were explained as nothing but conspicuous signals, the meaning of which the hen is able to decipher by help of her inherited instincts. The influence of the display is amongst these species undoubtedly strengthened by an action which is quite independent of any sexual associations. Besides accentuating the sex and kind of the cock, these luminous spheres will, moreover, in virtue of their very smallness and brilliancy, provoke a stimulation in the mind of the hen before whom they are vibrated. To understand this effect, it is necessary to investigate the more general question of animal appreciation of brilliancy. The powerful attraction exercised by lucent things can be sufficiently proved by numerous instances from the life of insects and fishes as well as of higher animals. It is needless to dwell upon the various means by which man has availed himself of this disastrous predilection in order to entice animals within reach of his weapons.[277] More important in this connection is the mania for collecting lustrous objects that has been noticed in the case of ravens, jays, magpies, jackdaws, goldfinches, chiff-chaffs, sea-pies, etc.[278] It has scarcely ever been suggested that the thievish jackdaw is prompted by any _æsthetic_ liking for brilliant plate. But as it shows itself amongst the atlas birds and the bower birds, this exaggeration of the appropriative impulse has been regarded as an indication of artistic inclination. It has been contended that these birds not only appreciate shining and gorgeous objects, but even understand how to arrange them according to a decorative plan.[279]