Spots and Stripes. 47 



hues of day-flying butterflies and moths than of the night-flying 

 species. Now, the sombre hues of nocturnal moths are not so much 

 protective (like the sober tints of female butterflies and birds), 

 because night and darkness is their great defender, as the necessary 

 result of the darkness : bright colours are not produced, because 

 they could not be seen and appreciated. In these cases it is very 

 noticeable how frequently the colour is irregularly dotted about — 

 irrorated or peppered over the wings, as it were. This irregular 

 distribution of the pigment cells, if it were quite free from any 

 arrangement, might be looked upon as primitive colouring, undiffer- 

 entiated either into distinct colour or distinct pattern. If we 

 suppose a few of the pigment cells here and there to become 

 coloured, we should have irregular brilliant dottings, just as we 

 actually see in many butterflies, along the costa. The grouping 

 together of these colour dots would give rise to a spot, from which 

 point all is clear. 



That some such grouping or gathering together, allied to segre- 

 gation, does take place, a study of spots, and especially of eye-spots, 

 renders probable. What the nature of the process is we do not 

 know, nor is it easy to imagine. But let us suppose a surface 

 uniformly tinted brown. Then, if we gather some of the colouring 

 matter into a dark spot we shall naturally leave a lighter area 

 around it, just as we see in all our Browns and Ringlets. In this 

 way we can see how a ring-spot can be formed. To make it a true 

 eye-spot, with a light centre, we must also suppose a pushing away 

 of the colour from that centre. A study of ocelli naturally suggests 

 such a process, which is analogous to the banding of agates, and all 

 concentric nodules. Darwin, struck with this, seems to adopt it as 

 a fact, for he says, " Appearances strongly favour the belief that, on 

 the one hand, a dark spot is often formed by the colouring matter 

 being drawn towards a central point from a surrounding zone, which 

 is thus rendered lighter. And, on the other hand, a white spot is 

 often formed by the colour being driven away from a central point, 

 so that it accumulates in a surrounding darker zone."* The analogy 

 between ocelli and concretions may be a real one. At any rate beauti- 

 ful ocelli of all sizes can be seen forming in many iron-stained sand- 

 stones. The growth of ocelli may thus be a mechanical process 

 adapted by the creature for decorative purposes, but the artistic 

 colouring of many eye-spots implies greater effort. 



* Desc. Man, vol. ii., p. 134. 



