Bk I:689-721 Mercury tells the story of Syrinx.
So the god explained, "On Arcadia's cold mountain slopes among the wood nymphs, the hamadryads, of Mount Nonacris, one was the most celebrated: the nymphs called her Syrinx. She had often escaped from the satyrs chasing her, and from others of the demi-gods that live in shadowy woods and fertile fields. But she followed the worship of the Ortygian goddess in staying virgin. Her dress caught up like Dianashe deceives the eye, and could be mistaken for Leto's daughter, except that her bow is of horn, and the other's is of gold. Even so she is deceptive. Pan, whose head is crowned with a wreath of sharp pine shoots, saw her, coming from Mount Lycaeus, and spoke to her." Now Mercury still had to relate what Pan said, and how the nymph, despising his entreaties, ran through the wilds till she came to the calm waters of sandy Ladon; and how when the river stopped her flight she begged her sisters of the stream to change her; and how Pan, when he thought he now had Syrinx, found that instead of the nymph's body, he only held reeds from the marsh; and, while he sighed there, the wind in the reeds, moving, gave out a clear, plaintive sound. Charmed by this new art and its sweet tones, the god said, "This way of communing with you is still left to me." So unequal lengths of reed, joined together with wax, preserved the girl's name.
About to tell all this, Cyllenian Mercury saw that every eye had succumbed and their light was lost in sleep. Quickly he stops speaking and deepens their rest, caressing those drowsy eyes with touches of his magic wand. Then straightaway he strikes the nodding head, where it joins the neck, with his curved sword, and sends it bloody down the rocks, staining the steep cliff. Argus, you are overthrown, the light of your many eyes is extinguished, and one dark sleeps under so many eyelids.