58 On the Production of Colour in Birds' Eggs. 



and the consequent impression upon the mental organisation 

 of the parents. This peculiarity of colour, too, has been of 

 service in rendering the eggs less easy of detection, as being 

 of neutral hues, or as resembling, more or less, the water 

 around or near the nest. 



But the brightest blues of all occur, very exceptionally, 

 in groups of birds of totally different habits, in no way 

 adapted to an aquatic life. Such are, for instance, amongst 

 English birds, the thrush and the starling, the hedge 

 sparrow and lesser redpole, the wheatear, and to a less 

 extent, the stone-chat and whin-chat. Amongst Australian 

 birds, are those of the naturalised Indian or Ceylon mynah, 

 the coach-whip bird, and the wedge-bill, and the species of 

 Zosterops, a small family allied to the honey-eaters. Such 

 examples, it is to be noted, are extremely scarce. It is 

 difficult to surmise the causes which can have combined to 

 produce this unique coloration. If the " motive " be pro- 

 tection, it must fall under the general principle, that 

 intruders are shy of the brightly coloured objects. Some 

 support for this view may be derived from Mr. Bates' well- 

 known observations on deterrent colours amongst insects. 

 It is difficult, moreover, to discover a blue in the surround- 

 ings of the birds, which could produce so pronounced a 

 mental conception of this colour. It may be the blue of the 

 butterflies on which they feed. It may be the blue of the 

 aerial vault above. It would seem, if this second suggestion 

 be the right one, that very few indeed of the birds have 

 their attention attracted strongly by the azure of the skies, 

 while they occupy their aerial homes. 



The eggs of the ostrich vie in colour with the pale yellow 

 sand of the African desert, in which they are buried for the 

 sake of incubation by the sun's heat ; but those of the emu, 

 laid in the Australian bush, are, as every one knows, dark 

 green. Here we have an indication that the Australian 

 bush is not made up of yellow sandy deserts. The emu, in 

 fact, scoops out a hole in the ground amongst low scrub, and 

 contemplates eucalypts and salt-bush, and other dull vegeta- 

 tion. Its eggs are exposed and protected by their colour. 

 The cassowary, laying and living amongst the bright green 

 of the tropical grasses, and the vivid green of a more 

 diversified tropical foliage, produces Hghter and brighter 

 green eggs. 



With the birds of prey the mental perception of habitual 

 surroundings seems to have been intense (as might have been 



