The results of surgical experiments show that the eyespot
in both P. coenia and B. anynana is specified from a central
signalling region or ‘‘focus’’ (Fig. 3A, B). Hence damage to the
focus in the early pupa removes (or shrinks) the entire
eyespot. More critically, transplanting the focus to another
position on the early pupal wing induces a concentric eyespot
pattern to form ectopically, in the epidermis surrounding the
graft(29–33) and this response may differ dramatically across
the wing epidermis (Fig. 3B). Also, on some wing surfaces,
local damage to the epidermis can mimic the focal signal,
inducing the formation of an ectopic eyespot (Fig. 3A,iv).(31,32,34)
Nijhout(29) suggested that the eyespot focus may act as a
local source that generates a conical morphogen gradient
extending over the surrounding epidermis, with different
concentrations specifying concentric rings within which the
scale cells later synthesise different pigments. In grafting
experiments using foci taken from the anterior (small) or
posterior (large) eyespot in B