Many of these estimates are, as will be seen, very vague and doubtful, so that we must still admit with Bacon that, "touching the length and shortness of life in living creatures, the information which may be had is but slender, observation is negligent, and tradition fabulous. In tame creatures their degenerate life corrupteth them, in wild creatures their exposing to all weathers often intercepteth them." ON INDIVIDUALITY When we descend still lower in the animal scale, the consideration of this question opens out a very curious and interesting subject connected with animal individuality. As regards the animals with which we are most familiar no such question intrudes. Among quadrupeds and birds, fishes and reptiles, there is no difficulty in deciding whether a given organism is an individual, or a part of an individual. Nor does the difficulty arise in the case of most insects. The Bee or Butterfly lays an egg which develops successively into a larva and pupa, finally producing Bee or Butterfly. In these cases, therefore, the egg, larva, pupa, and perfect Insect, are regarded as stages in the life of a single individual. In certain gnats, however, the larva itself produces young larvae, each of which develops into a gnat, so that the egg produces not one gnat but many gnats. The difficulty of determining what constitutes an individual becomes still greater among the Zoophytes. These beautiful creatures in many cases so closely resemble plants, that until our countryman Ellis proved them to be animals, Crabbe was justified in saying-- Involved in seawrack here we find a race, Which Science, doubting, knows not where to place; On shell or stone is dropped the embryo seed, And quickly vegetates a vital breed. We cannot wonder that such organisms were long regarded as belonging to the vegetable kingdom. The cups which terminate the branches contain, however, an animal structure, resembling a small Sea Anemone, and possessing arms which capture the food by which the whole colony is nourished. Some of these cups, moreover, differ from the rest, and produce eggs. These then we might be disposed to term ovaries. But in many species they detach themselves from the group and lead an independent existence. Thus we find a complete gradation from structures which, regarded by themselves, we should unquestionably regard as mere organs, to others which are certainly separate and independent beings. [Illustration: Fig. 2.--Bougainvillea fruticosa; natural size. (After Allman.)]