This paper integrates genetical studies of variation in the wing patte
rns of Lepidoptera with experimental investigations of developmental m
echanisms. Research on the tropical butterfly, Bicyclus anynana, is de
scribed. This work includes artificial selection of lines with differe
nt patterns of wing eyespots followed by grafting experiments on the l
ines to examine the phenotypic and genetic differences in terms of dev
elopmental mechanisms. The results are used to show how constraints on
the evolution of this wing pattern may be related to the developmenta
l organisation. The eyespot pattern can be envisaged as a set of devel
opmental homologues; a common developmental mechanism is associated wi
th a quantitative genetic system involving high genetic correlations.
However, individual genes which influence only subsets of the eyespots
, thus uncoupling the interdependence of the eyespots, may be importan
t in evolutionary change. The postulated evolutionary constraints are
illustrated with respect to differences in wing pattern found among ot
her species of Bicyclus.