"Bunny had heard that John Donne had been acquainted with Izaak Walton"

 Izaak Walton (1593-1683) was an English writer, a friend of John Donne who wrote a short biography of him (which can be read online here). However the two men were quite different; whilst Donne is best known for his Metaphysical poems, Walton is known for his book The Compleat Angler, a celebration of the art of fishing. They are certainly not, as Bunny posits, deeply connected through 'metahemeralism', as this is not in fact a real word.