And if the privilege of scepticism is hope, the essence of it is questioning and questing. There is a doubt which, in its despair of ultimate truth, is content to trifle, to beguile the misery of life with jest and play and momentary diversion. Or there is the doubt in deeper matters which, as with Darwin, turns to eager, assiduous investigation of the mere, fascinating detail of the external world. But there is also a doubt which lives in passionate, perpetual earnestness and the unfailing, unyielding, indomitable effort to find out God, being assured that without Him the universe, with all its splendor and all its endless evolving glory, is nothing, merely nothing. Such doubt will express itself in words like those of the modern poet: ‘Day and night I wander widely through the wilderness of thought, Catching dainty things of fancy most reluctant to be caught. Shining tangles leading nowhere I persistently unravel, Tread strange paths of meditation very intricate to travel. Gleaming bits of quaint desire tempt my steps beyond the decent. I confound old solid glory with publicity too recent. But my one unchanged obsession, whereso’er my feet have trod, Is a keen, enormous, haunting, never-sated thirst for God.’ THE END BOOKS BY DARWIN, WITH THE ABBREVIATIONS USED IN REFERRING TO THEM IN THE NOTES The American revised edition is referred to, unless otherwise specified _A Monograph on the sub-class Cirripedia.—The Balanidæ—The Verrucidæ._ _Cirripedia._ _The Descent of Man and Selection in Relation to Sex._ _Descent._ _The Different Forms of Flowers on Plants of the Same Species._ _Different Forms of Flowers._ _The Effects of Cross and Self Fertilization in the Vegetable Kingdom._ _Cross and Self Fertilization._ Krause, Ernst, _Erasmus Darwin_ (translated from the German by W. S. Dallas, with a preliminary notice by Charles Darwin). _Krause._ _The Expression of the Emotions in Man and Animals._ _Expression._ _The Formation of Vegetable Mould through the Action of Worms._ _Worms._ _Geological Observations._ _Geological Observations._ _Insectivorous Plants._ _Insectivorous Plants._ _Journal of Researches into the Natural History and Geology of the Countries Visited during the Voyage of H.M.S. Beagle Round the World._ _Beagle Journal._ _More Letters of Charles Darwin_, two volumes. _More Letters._ _The Movements and Habits of Climbing Plants._ _Climbing Plants._ _The Origin of Species._ _Origin._ _The Power of Movement in Plants._ _Movement in Plants._ _The Variation of Animals and Plants under Domestication_, two volumes. _Animals and Plants._ _The Various Contrivances by which Orchids are Fertilized by Insects._ _Orchids._ BOOKS BIOGRAPHICAL AND CRITICAL MOST FREQUENTLY REFERRED TO IN THE NOTES, WITH THE ABBREVIATIONS USED Aristotle, _Historia Animalium_, translated by D’Arcy Wentworth Thompson. _Historia Animalium._ Castle, W. E., _Genetics and Eugenics_. _Genetics and Eugenics._