Really! So, to avoid slow and painful work, to achieve an easy life, to give herself the leisure favourable to the settlement of her family, the erstwhile cotton-presser or collector of resin-drops took to gnawing hardened cement! She who once sipped the nectar of flowers made up her mind to chew concrete! Why, the poor wretch toils at her filing like a galley-slave! She spends more time in ripping up a cell than it would take her to make a cotton wallet and fill it with food. If she really meant to progress, to do better in her own interest and that of her family, by abandoning the delicate occupations of the old days, we must confess that she has made a strange mistake. The mistake would be no greater if fingers accustomed to fancy-weaving were to lay aside velvet and silk and proceed to handle the quarryman's blocks or to break stones on the roadside. No, the animal does not commit the folly of voluntarily embittering its lot; it does not, in obedience to the promptings of idleness, give up one condition to embrace another and a more irksome; should it blunder for once, it will not inspire its posterity with a wish to persevere in a costly delusion. No, the Stelis never abandoned the delicate art of cotton-weaving to break down walls and to grind cement, a class of work far too unattractive to efface the memory of the joys of harvesting amid the flowers. Indolence has not evolved her from an Anthidium. She has always been what she is to-day: a patient artificer in her own line, a steady worker at the task that has fallen to her share. That hurried mother who first, in remote ages, broke into the abode of her fellows to secure a home for her eggs found this unscrupulous method, so you tell us, very favourable to the success of her race, by virtue of its economy of time and trouble. The impression left by this new policy was so profound that heredity bequeathed it to posterity, in ever-increasing proportions, until at last parasitic habits became definitely fixed. The Chalicodoma of the Sheds, followed by the Three-horned Osmia, will teach us what to think of this conjecture. I have described in an earlier chapter my installation of Chalicodoma-hives against the walls of a porch facing the south. Here, on a level with my head, placed so that they can easily be observed, hang some tiles removed from the neighbouring roofs in winter, together with their enormous nests and their occupants. Every May, for five or six years in succession, I have assiduously watched the works of my Mason-bees. From the mass of my notes on the subject I take the following experiments which bear upon the matter under discussion.