reflexed hairs allow small flies to creep in, but effectually prevent their escape until they have fertilised the pistils, when the hairs relax. These are only specimens of a multitude of adaptations which fill the book. Sprengel insists upon the study of flowers under natural conditions; he could never have made out by the examination of plucked flowers how Nigella is fertilised. Flies with attached pollen-masses, which he found in spiders' nests, gave him the hint as to the way in which the fertilisation of orchids is effected. Definite questions must be put if observation is to be profitable. What is the use of honey to the plant—of this coloured spot—of these hairs? He notes the peculiarities of wind-fertilised and insect-fertilised flowers, the relative abundance of the pollen, the form of the stigma, the presence or absence of honey, the size, colour, and scent of the corolla. Here is a pretty illustration from his pages. Pluck a branch of hazel, aspen, or alder, with unexpanded catkins, and also one from the male sallow; place them in water, and keep them in a sunny window until the anthers are ripe. A vigorous puff will then discharge a cloud of pollen from the _wind-fertilized_ catkins, but none from the _insect-fertilised_ catkin of the sallow. What Linnæus said about the flowers of trees appearing before the leaves, in order that the pollen may more easily reach the stigmas, holds good, Sprengel remarks, only of wind-fertilised trees. The lime, which is insect-fertilised, flowers in the height of summer, when all the branches are crowded with leaves. Sprengel left it to later biologists to complete his discovery. "That wonderfully accurate observer, Sprengel," says Darwin,[32] "who first showed how important a part insects play in the fertilisation of flowers, called his book _The Secret of Nature Displayed_; yet he only occasionally saw that the object for which so many curious and beautiful adaptations have been acquired, was the cross-fertilisation of distinct plants; and he knew nothing of the benefits which the offspring thus receive in growth, vigour, and fertility." Not even Cuvier and the Rise of Palæontology. If this historical sketch had been prepared within a few years of the death of Cuvier, it would no doubt have held him up as the greatest of zoologists and comparative anatomists. Nor would it have been hard to find reasons for such a verdict. His _Règne Animal_ extended and corrected the zoological system of Linnæus; his comparative anatomy, and especially his comparative osteology, were far ampler and more exact than anything that had been attempted before. It would not have been forgotten, moreover, that he was the practical founder of the new science of palæontology.