There are two epigraphs to the third section of "Carnivals," which follow the "Postcard" quatrains.
In The Consuming Myth, Yenser explains that one of the prose quotations is "attributed to [Merrill's] friend Germaine Nahman, the other to a mythical book by a mythical author, Psyche's Sisters by A. H. Clarendon" (130). "Clarendon" is also quoted in section "Q" of The Book of Ephraim from another invented book, Time Was.
Nahman wrote from Paris on March 11, 1963 to give her permission for The New Yorker to publish her name as the (fictitious) author of the passage.
Langdon Hammer in James Merrill: Life and Art (Knopf 2015) observes that the Nahman passage
provides an allegorical interpretation of Merrill’s "grotesque" sexual pursuits. Here he links the libertine’s quest for stimulation and pleasure, as he would much later in The Changing Light at Sandover, to man’s abuse of the planet: "Likewise, upon Earth’s mature body we inflict a wealth of gross experience— drugs, drills, bombardments— with what effect? A stale frisson, a waste of resources all too analogous to our own. Natural calamities (tumor and apoplexy no less than flood and volcano) may at last be hailed as positive reassurances, perverse if you like, of life in the old girl yet."
By a clever turn, Merrill comes around to saying that his symptoms are a positive reassurance of life in him yet. The idea is enough for him to proclaim, slipping into verse again, the recovery of love. But he backs away from this affirmation as soon as he makes it, suspicious of his own rhetorical powers, his too-easy wish for a simple, decent, sunlit solution . . . (pp. 325-26).