The attempt to explain dreams of flying has led to some bold hypotheses. Freud characteristically affirms that the dream of flying is the bridge to a concealed wish.[109] I have already mentioned the notion that dreams of flight are excursions of the 'astral body.' Professor Stanley Hall, who has himself, from childhood, had dreams of flying, argues, with scarcely less boldness, that we have here 'some faint reminiscent atavistic echo from the primeval sea'; and that such dreams are really survivals--psychic vestigial remains comparable to the rudimentary gill-slits not uncommonly found in man and other mammals--taking us back to the far past when man's ancestors needed no feet to swim or float.[110] Such a theory may accord with the profound conviction of reality that accompanies these dreams, though that may be more easily accounted for; but it has the very serious weakness that it offers an explanation which will not fit the facts. Our dreams are of flying, not of swimming; but the ancestors of the mammals probably lived in the water, not in the air. In preference to so hazardous a theory, it seems infinitely more reasonable to regard these dreams as an interpretation--a misinterpretation from the standpoint of waking life--of actual internal sensations. If we can find the adequate explanation of a psychic state in conditions actually existing within the organism itself at the time, it is needless to seek an explanation in conditions that ceased to exist untold millenniums ago.