Far in the past before Atlantis existed,
men there were who delved into darkness,
using dark magic, calling up beings
from the great deep below us.
Forth came they into this cycle.
Formless were they of another vibration,
existing unseen by the children of earth-men.
Only through blood could they have formed being.
Only through man could they live in the world.
In ages past were they conquered by Masters,
driven below to the place whence they came.
But some there were who remained,
hidden in spaces and planes unknown to man.
Lived they in Atlantis as shadows,
but at times they appeared among men.
Aye, when the blood was offered,
for they came they to dwell among men.
In the form of man they amongst us,
but only to sight were they as are men.
Serpent-headed when the glamour was lifted
but appearing to man as men among men.
Crept they into the Councils,
taking forms that were like unto men.
Slaying by their arts
the chiefs of the kingdoms,
taking their form and ruling o'er man.
Only by magic could they be discovered.
Only by sound could their faces be seen.
Sought they from the Kingdom of shadows
to destroy man and rule in his place.
I read this in the internet version of The Emerald Tablets of Thoth
which purports to be the writings of Thoth, the builder of the Great Pyramid of Giza. It appears to be a description of reptilian shapeshifters in the manner mentioned by David Icke.
The actual quote is from Tablet VIII, The Key of Mystery