IX 
THE MARKINGS OF ORGANISMS 
203 
logous parts tend to behave in the colour scheme as 
do the successive segments in little differentiated 
forms. So close, however, is the relation between 
structure and colour, that differential growth of the 
wings resulting in the overlapping of parts is also 
accompanied by corresponding change of pattern. 
This is well seen in many butterflies where the fore¬ 
wings overlap the hind. We have already noticed 
the peculiar case described by Sharp in which the 
fore-wings of an orthopterous insect differed from one 
another in their colouring, but the irregularity was 
corrected in the position of rest by the overlapping 
of parts. It is a curious example of that detailed 
relation which exists between colour-markings and 
structure. 
In spite of the conspicuousness of colour-markings 
in many insects, there seems as yet no certainty as 
to the proximate cause or meaning of the patterns. 
Over the markings of caterpillars, their meaning and 
their evolution, it is true that many fierce controversies 
have raged ; but the questions as to whether longi¬ 
tudinal or transverse markings are the most primitive, 
the number of the possible longitudinal stripes, their 
use, and the kindred questions seem to be decided so 
much by the caprice of the individual investigator, 
that a non-specialist may be permitted to retire from 
the field until the parties concerned have been able 
to patch up some sort of a truce. 
Mollusca .—In the Mollusca colour-patterns are, 
except in the cuttles, confined to the shells, in which 
banding is very common, and is well seen in common 
snails {Helix). More elaborate schemes of ornamenta¬ 
tion are not uncommon, and are not infrequently 
