Among the earliest drawings on Greek vases it is not rare to find a lion, for example, or a bird with apparently two bodies and only one head between them, as in Figs. 1–2. (Pl. XV.) After a long interval a similar rendering of animal form occurs no less frequently in Roman work, as in the sphinx, Fig. 4. So long as this curious proceeding in the art of design was thought to be the outcome of fancy, no explanation of it was sought for. Curtius, however, had found from many observations, that Assyrian, Phoenician, and early Greek designs, were largely influenced by a principle of dualism, displaying itself mostly in devices which consist of a group of two animals confronted, the one responding strictly to the other in form and action, much as the impression of a seal responds to the seal itself. In early times when seals were employed to an extent hardly to be realized now, it may seem to have been easy and natural for an engraver or other designer to have observed and utilised the peculiarly decorative effect obtained from the contrast of a seal with its impression.