eidolon

As a species it is extinct; as an eidolon it retains its corporeality – but only if maintained in a state of equipoise.

Was Philippe d'Orleans seen, this day, 'in the Bois de Boulogne, in grey surtout;' waiting under the wet sere foliage, what the day might bring forth? Alas, yes, the Eidolon of him was,—in Weber's and other such brains.