Necronomicon- Shoggoths

It was under the sea, at first for food and later for other purposes, that they first created earth-life—using available substances according to long-known methods. The more elaborate experiments came after the annihilation of various cosmic enemies. They had done the same thing on other planets; having manufactured not only necessary foods, but certain multicellular protoplasmic masses capable of moulding their tissues into all sorts of temporary organs under hypnotic influence and thereby forming ideal slaves to perform the heavy work of the community. These viscous masses were without doubt what Abdul Alhazred whispered about as the “shoggoths” in his frightful Necronomicon, though even that mad Arab had not hinted that any existed on earth except in the dreams of those who had chewed a certain alkaloidal herb. When the star-headed Old Ones on this planet had synthesised their simple food forms and bred a good supply of shoggoths, they allowed other cell-groups to develop into other forms of animal and vegetable life for sundry purposes; extirpating any whose presence became troublesome.
     With the aid of the shoggoths, whose expansions could be made to lift prodigious weights, the small, low cities under the sea grew to vast and imposing labyrinths of stone not unlike those which later rose on land. Indeed, the highly adaptable Old Ones had lived much on land in other parts of the universe, and probably retained many traditions of land construction.
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I came only just short of echoing his cry myself; for I had seen those primal sculptures, too, and had shudderingly admired the way the nameless artist had suggested that hideous slime-coating found on certain incomplete and prostrate Old Ones—those whom the frightful shoggoths had characteristically slain and sucked to a ghastly headlessness in the great war of re-subjugation. They were infamous, nightmare sculptures even when telling of age-old, bygone things; for shoggoths and their work ought not to be seen by human beings or portrayed by any beings. The mad author of the Necronomicon had nervously tried to swear that none had been bred on this planet, and that only drugged dreamers had ever conceived them. Formless protoplasm able to mock and reflect all forms and organs and processes—viscous agglutinations of bubbling cells—rubbery fifteen-foot spheroids infinitely plastic and ductile—slaves of suggestion, builders of cities—more and more sullen, more and more intelligent, more and more amphibious, more and more imitative—Great God! What madness made even those blasphemous Old Ones willing to use and to carve such things?

- At the mouth of Madness, parts VII and XI