the need for an as yet unknown moth with a proboscis 10–11 inches (250–275 mm) long to pollinate these flowers in Madagascar. He viewed this as the outcome of a coevolutionary race, writing that "there has been a race in gaining length between the nectary of the Angræcum and the proboscis of certain moths". This wastefulness is familiar in modern terms as the idea of an evolutionary arms race, but was disturbing to biologists of the time who believed that adaptations were the outcome of benevolent divine purpose. Darwin described "the most remarkable of all Orchids", Catasetum, and showed how in these flowers, "as throughout nature, pre-existing structures and capacities [had been] utilised for new purposes". He explained the mechanism in which the pollen masses of the pollinium were connected by a bent stalk or pedicel to a sticky disc kept moist at the back of the flower. When an insect touched an "antenna" projecting from the back of the flower, this released the bent pedicel which sprang straight and fired the pollinium, sticky disc first, at the insect. In experiments, Darwin had imitated this action using a whalebone spring. He vividly illustrated how the flower ejected the pollinium with considerable force: "I touched the antennæ of C. callosum whilst holding the flower at about a yard's distance from the window, and the pollinium hit the pane of glass, and adhered to the smooth vertical surface by its adhesive disc." Final chapter Darwin noted that the essential nectar, secreted to attract insects, seemed also in some cases to act as an excretion: "It is in perfect accordance with the scheme of nature, as worked out by natural selection, that matter excreted to free the system from superfluous or injuring substances should be utilised for purposes of the highest importance." Homologies of the flowers of orchids showed them all to be based on "fifteen groups of vessels, arranged three within three, in alternating order". He disparaged the idea that this was an "ideal type" fixed by the Omnipotent Creator, but attributed it instead to its "descent from some monocotyledonous plant, which, like so many other plants of the same division, possessed fifteen organs, arranged alternately three within three in five whorls; and that the now wonderfully changed structure of the flower is due to a long course of slow modification,—each modification having been preserved which was useful to each plant, during