CHAPTER XVIII THE HAIRY AMMOPHILA 323 CHAPTER XIX AN UNKNOWN SENSE 341 CHAPTER XX THE MODERN THEORY OF INSTINCT 354 APPENDIX 379 CHAPTER I THE BUPRESTIS-HUNTING CERCERIS There are for each one of us, according to his turn of mind, certain books that open up horizons hitherto undreamed of and mark an epoch in our mental life. They fling wide the gates of a new world wherein our intellectual powers are henceforth to be employed; they are the spark which lights the fuel on a hearth doomed, without its aid, to remain indefinitely bleak and cold. And it is often chance that places in our hands those books which mark the beginning of a new era in the evolution of our ideas. The most casual circumstances, a few lines that happen somehow to come before our eyes, decide our future and plant us in the appointed groove. One winter evening, when the rest of the household was asleep, as I sat reading beside a stove whose ashes were still warm, my book made me forget for a while the cares of the morrow: those heavy cares of a poor professor of physics who, after piling up diplomas and for a quarter of a century performing services of uncontested merit, was receiving for himself and his family a stipend of sixteen hundred francs, or less than the wages of a groom in a decent establishment. Such was the disgraceful parsimony of the day where education was concerned; such was the edict of our government red-tape: I was an irregular, the offspring of my solitary studies. And so I was forgetting the poverty and anxieties of a professor’s life, amid my books, when I chanced to turn over the pages of an entomological essay that had fallen into my hands I forget how. It was a monograph by the then father of entomology, the venerable scientist Léon Dufour, [1] on the habits of a Wasp that hunted Buprestis-beetles. Certainly, I had not waited till then to interest myself in insects; from my early childhood I had delighted in Beetles, Bees, and Butterflies; as far back as I can remember, I see myself in ecstasy before the splendour of a Ground-beetle’s wing-cases or the wings of Papilio machaon, the Swallowtail. The fire was laid; the spark to kindle it was absent. Léon Dufour’s essay provided that spark.