Jack London, The Iron Heel, 1908
During that period I used to marvel at my own metamorphosis. At times it seemed impossible, either that I had ever lived a placid, peaceful life in a college town, or else that I had become a revolutionist inured to scenes of violence and death. One or the other could not be. One was real, the other was a dream, but which was which? Was this present life of a revolutionist, hiding in a hole, a nightmare? or was I a revolutionist who had somewhere, somehow, dreamed that in some former existence I have lived in Berkeley and never known of life more violent than teas and dances, debating societies, and lectures rooms?
'Formerly, I, Kwang Kâu, dreamt that I was a butterfly, a butterfly flying about, feeling that it was enjoying itself. I did not know that it was Kâu. Suddenly I awoke, and was myself again, the veritable Kâu. I did not know whether it had formerly been Kâu dreaming that he was a butterfly, or it was now a butterfly dreaming that it was Kâu. But between Kâu and a butterfly there must be a difference. This is a case of what is called the Transformation of Things.'
Translation by James Legge (1815-1897)
Of course, we might also consider the opening lines of Franz Kafka's, The Metamorphosis, written in 1916, the same year London passed away:
One morning, as Gregor Samsa was waking up from anxious dreams, he discovered that in bed he had been changed into a monstrous verminous bug. He lay on his armour-hard back and saw, as he lifted his head up a little, his brown, arched abdomen divided up into rigid bow-like sections. From this height the blanket, just about ready to slide off completely, could hardly stay in place. His numerous legs, pitifully thin in comparison to the rest of his circumference, flickered helplessly before his eyes.
"What's happened to me," he thought. It was no dream. His room, a proper room for a human being, only somewhat too small, lay quietly between the four well-known walls.
UPDATE: For anyone interested in the connection between Chinese thought and Kafka's writing, here is a link to Kafka's, The Great Wall of China. While conducting a google search on "Kafka and Zhuangzi" I found someone in Macau, Christopher Kelen, who is asking similar questions about Kafka, butterflies, The Great Wall of China, and my favorite--The Peach Blossom Spring
Kelen writes about butterflies as follows:
One of the beautiful clichés of Chinese thought which Westerners love to appropriate (witness Kronenburg's M. Butterfly) is Zhuangzi's parable of one Zhuang Zhou who dreamt he was a butterfly and forgot he was a person. Zhuangzi asks us whether Zhuang Zhou dreamt of the butterfly or the butterfly dreamt of Zhuang Zhou. The story has parallels in Western thought: notably in the Meditations of Descartes and in Alice's speculations in Through the Looking Glass. A twentieth century example is in Borges' story 'The Circular Ruins'. In each case reflexive aim at identity is taken by positing contrast between reality and a state of mind in which one wouldn't know one's self or one's state of mind.
Implied in these fancies is another world in which what we know for reality is somehow upended, a world in which the rules of the real do not or need not apply. It's easy to see the model (and/or the need) for worlds which may collectively be thought of as fictional in the universal diurnal event of dreaming.