Arthur E. Waite - The Pictorial Key to the Tarot :
The distinction between this card and some of the conventional types is that the moon is increasing on what is called the side of mercy, to the right of the observer. It has sixteen chief and sixteen secondary rays.
The card represents life of the imagination apart from life of the spirit. The path between the towers is the issue into the unknown. The dog and wolf are the fears of the natural mind in the presence of that place of exit, when there is only reflected light to guide it.
The last reference is a key to another form of symbolism. The intellectual light is a reflection and beyond it is the unknown mystery which it cannot shew forth. It illuminates our animal nature, types of which are represented below - the dog, the wolf and that which comes up out of the deeps, the nameless and hideous tendency which is lower than the savage beast.
It strives to attain manifestation, symbolized by crawling from the abyss of water to the land, but as a rule it sinks back whence it came. The face of the mind directs a calm gaze upon the unrest below; the dew of thought falls; the message is: Peace, be still; and it may be that there shall come a calm upon the animal nature, while the abyss beneath shall cease from giving up a form.
P. D. Ouspensky – The Symbolism Of The Таrot :
A desolate plain stretched before me. A full moon looked down as if in contemplative hesitation. Under her wavering light the shadows lived their own peculiar life. On the horizon I saw blue hills, and over them wound a path which stretched between two grey towers far away into the distance. On either side the path a wolf and dog sat and howled at the moon. I remembered that dogs believe in thieves and ghosts. A large black crab crawled out of the rivulet into the sands. A heavy, cold dew was falling.
Dread fell upon me. I sensed the presence of a mysterious world, a world of hostile spirits, of corpses rising from graves, of wailing ghosts. In this pale moonlight I seemed to feel the presence of apparitions; someone watched me from behind the towers,--and I knew it was dangerous to look back.