There is, however, one set of colour lines in birds and insects that do not seem to arise from spots in the ordinary way. These are the coloured feather-shafts of birds, and the coloured nerves or veins in a butterfly's wing, In these the colour has a tendency to flow all along the structure in lines.
Conclusion. The results arrived at in this chapter may be thus summarised:—
Spots, ocelli, stripes, loops, and patches may be, and nearly always are, developed from more or less irregular spots.
This is shown both by the study of normal colouring, or by abnormal colouring, or decolouring in disease.
Even the celebrated case of the Argus Pheasant shows that the bands from which the ocelli are developed arose from spots.
[CHAPTER VII.]
Colouration in the Invertebrata.
I
IF the principle of the dependence of colour-pattern upon structure, enunciated in the preceding pages be sound, we ought to find certain great schemes of colouration corresponding to the great structural subdivisions of the animal kingdom. This is just what we do find; and before tracing the details, it will be as well to group the great colour-schemes together, so that a general view of the question can be obtained at a glance.
The animal kingdom falls naturally into two divisions, but the dividing line can be drawn in two ways. If we take the most simple classification, we have:—
1. Protozoa, animals with no special organs.
2. Organozoa, animals possessing organs.