A man had spiritual vision and knowledge in earlier stages of development. His body was a kind of resting place for him in which he could sleep and lose his consciousness while he was in it. As his being became increasingly conscious on the physical plane his spiritual perception and cognition decreased. When man became very interested in things around him he lost his spiritual vision and cognition entirely, and a dense veil covered spiritual things. This interest in outer sense phenomena is called estimatio in occultism, and estimatio is a poison that brings death. It takes away consciousness of the continued existence of the I and thereby brings a consciousness of birth and death with it. It blots out consciousness of the I and the memory of continued life. Consciousness must not be withdrawn from the outer world entirely, for then it wouldn't take the essence of what it gained from outer experiences with it. However this is the case in imagination. It must not be completely inactive; a man must be able to direct his consciousness at a picture of his action at will. A man wouldn't be able to raise his hand if he couldn't imagine it pictorially. When he raises his hand the picture and action are present simultaneously. If he begins to make mental images without an action, that is, if he unites his consciousness with the imagined picture he'll then regain the ability to see astral things. This stage is called imago. When the soul attains complete peace or quiet so that it remains completely peaceful no matter what approaches it, then its consciousness will be able to penetrate the veil of the harmony of the spheres. This means transmutatio through inspiritation or incatatio. When glands were created on old Sun it happened through a process that's similar to the one that takes place in our body when someone thinks of food and this makes his mouth water. Glands were created on old Sun by higher beings who, as it were, tasted the surroundings and secreted the gland substance that was absorbed by physical bodies. Adrenal glands secrete a substance that promotes bone building. The pancreas transforms sugar into substances that are good for nutrition. Secretion of the glands is a process that's brought about by soul processes.
When man lived in an astral or picture consciousness so that his spirit could go into spiritual realms at will, some beings remained at this stage. This stage remained crystallized in them, as it were, and birds represent this in a crystallized form. Birds like eagles who have such a wonderful eye, have crystallized astral vision. Mammals crystallized the stage where man tried to control his body's movements. These animals attained this only partially and therefore remained behind at a lower stage of evolution.