To test the
possibility of differential selection of colour morphs on different backgrounds,
colour proportions of juvenile and adult shells were compared on trees with
abundant foliage and on those with sparse foliage at the levels occupied by the
snails. Selection by the morphs of the background against which they are most
cryptic may promote polymorphism (Endler, 1978), so the distribution of shell
colours on bark and leaf substrates within trees was investigated.