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 



