When the creative and receptive powers of nature had thus been comprehended in the forms of Osiris and Isis, the divinities in whom creative power and receptivity had hitherto been perceived naturally coalesced with these forms to a greater or less degree. Thus Ptah of Memphis, Tum of Thebes, the sun-god of Heliopolis, are combined with Osiris (the title Ptah-Osiris is not uncommon in the inscriptions,) though they are also retained as separate deities. Thus also Isis is identified with Neith of Sais, with Mut of Thebes, with Hathor, with Bast,[89] the goddess of Bubastis. Horus, again, is identified with Chem and Ra, though at the same time his personality as the youthful, vigorous spirit of light is strongly marked. Plutarch is certainly right in his remark that the Egyptians regard Osiris as the personification of everything in heaven and the under world.[90] All the other deities were transfigurations and manifestations of Osiris, mere modifications of his nature. When Osiris is called the soul of Ra,[91] this can hardly have any other meaning but this, that the appearance of the sun-god in the visible world is an incarnation of the invisible nature of Osiris. The Egyptians often represented their deities with the heads, or in the shape of, the animals sacred to them; that is, they recognised the nature of the deities who were primarily conceived under the form of men, in the races of the beasts which they allotted to them. To the Egyptians these animals must have appeared so closely and intimately connected with the deity to which they belonged, that the nature of the deity was better expressed and made more visible in the shape of the beast than in the shape of man. We must assume that the predominance of a distinct mark or characteristic property in the races of animals, that their simple, uniformly instinctive life created this conception in the mind of the Egyptians, to whom a fixed and unalterable course of action, an unchanging and typical nature, was the ideal. The force of nature, the regular recurrence of certain phenomena, coalesced in the Egyptian mind with the blind, unchanging action of animals. Yet animals were also seen to possess freedom and movement, and an individual existence. This combination of the type and the individual must have seemed to the Egyptians to correspond to the nature of their deities. The mystery of life, the natural law, which lay at the base of their worship, must for them have reached its most distinct and lively realisation in these animals.