things to seize an advantage. Beasts of prey, many of them, sleep during the day, and steal forth at night on velvet foot to pounce on the slumbering animals which are their necessary food. Another group of timid animals, moths and small beasts like mice, hedgehogs, and lemurs, find their safety in the dark, and only then venture forth. Even so, the moths are met by special nocturnal enemies, the bats. So that the primitive arrangement is complicated by a wakefulness, exchanging day for night. It is natural to apply the word “sleep” to the state of profound repose which other living things appear to enter upon at night, so far as we can judge by changes of activity and attitude—although it must be remembered that the sleep of man is what we really indicate by that word, and that it is difficult to trace anything beyond a superficial similarity between man’s sleep and the repose or quiescence following upon activity in other living things—excepting those which by their structure and the working of their mechanism are obviously comparable to man, such as beasts, birds, reptiles, and fishes. The “sleep of plants” is the term applied to the closing of the flower, the drooping of the flower-head and of the leaves of many of the common flowering plants, which occurs at sunset or during the later hours of sunlight. But it seems that this is not really comparable to man’s sleep. The closing of the flower appears to be a protection of its perfume from useless evaporation during the darkness, and the drooping a device to avoid the settlement of dew and the injurious action of cold. Living things always furnish us with examples of adaptations resisting the general law—and as there are moths which fly by night, so also there are flowers which remain closed by day and open at night to attract these moths, by whom their pollen is carried and their fertilisation effected. The tobacco-plants of our gardens are examples of these night-opening flowers, which attract the nocturnal moths by their heavy perfume, and there are many others. The movements of plants are much more definite and varied than one is apt to suppose. Leaves and flowers turn to or away from the sun, or to or from the position which will favour a deposit of moisture; or, again, their tendrils will explore and seize upon supports, enabling them to secure a hold, and so to climb. The sensitive plant exhibits rapid drooping movements of its leaflets and leaf-stalks when touched or subjected to vibration.