437 
i88o.] The Laws of Emphasis and Symmetry . 
diffusive power of different colouring-matters. Everyone 
must have observed that if a coloured liquid, not too intense 
in its shade, — e.g., wine or tea,— is allowed to fall upon 
some white fibrous material, the spot produced will be 
darkest at the edges, whilst in the centre the linen or paper 
will scarcely appear stained. If, again, several colours 1 - 
fering in diffusibility are dissolved in the same liquid, they 
may "be to a certain extent separated from each other on the 
same principle. Thus in the earlier days of the manufacture 
of the aniline dyes, samples were often met with which 
from inattention or from imperfect purification— consisted ot 
two or more colouring-matters mixed together, i o detect 
such mixtures it was usual to place a drop of the solution on 
a sheet of white blotting-paper, when the different, colours 
appeared as concentric rings. If we suppose the tmctoria 
matters present in the fluids of the butterfly towards the 
close of its pupa-life being liberated in the porous tissues ot 
the wings, we can form some remote conception ot the 
manner in which these patterns are produced. 
It will perhaps, however, be asked^ by some naturalists 
whether the parts where these borde'rings chiefly occur— 
i,e wings and elytra — can fairly be pronounced impoitan 
parts ” in the same sense as is the central axis in vertebrate 
animals ? Mr. Wallace* points out as a remarkable tact 
that black spots, ocelli, and bright patches of colour aie 
generally on the tips, margins, or disks of the wings, at a 
distance from the vital organs, and considers that this 
position of the more conspicuous parts may be a protection 
to the insedts. . , . . , 
In vertebrate animals Mr. Tylor considers that empha- 
sised ornamentation has what he calls an axial character, 
“ being the outward expression of the central axis or verte- 
bral column with its appendages.” It is perfectly corredt 
that in a vast number of vertebrates the head is prominently 
decorated, and in many mammals and reptiles the back is 
adorned with stripes, or chains of spots, from which other 
stripes branch off at right angles, or nearly so, to the main 
axis of the body. In birds I believe a dorsal stripe, it it 
occurs at all, is very rare. This design, in which the con- 
trasting colours are often very striking, is referred to in e 
“Journal of Science,” t and is there traced much. more 
widely among Articulata than among vertebrate animals. 
• “ Colours of Animals and Plants,” in Macmillan’s Magazine, No. 215, 
D. 402. c 
f February, 1879, p. 19^ and July, 1879, p. 4Qo» 
