One of the water-plants of Southern Europe, _Aldrovandia vesiculosa_, which is also to be found in swamps on the northern ridge of the Alps, possesses, in addition to the capturing and digesting apparatus proper, an active motile apparatus, which is set in motion through sensitive hairs. When I found the plant for the first time in a swamp at Lindau, on the Lake of Constance, I took it at first sight for an _Utricularia_, for the two plants resemble each other in external appearance (cf. Figs. 22 and 29), but the modification of the leaves into traps is quite different. On both halves of the leaf-blade there are numerous bristles (Fig. 30, _A_), and the lightest touch on these by a little water animal acts as a releasing stimulus to the motile elements of the leaf (_Stch_). As in the Venus fly-trap, the two halves of the leaf close together somewhat quickly, but quite quietly, and the animal is caught. Fig. 30 shows a section of one of these traps in its closed state. The captive animals cannot escape, because the margins of the leaf shut quite tightly on one another, and are beset with little teeth. Numerous little glands (_Dr_) secrete a digestive juice, and after some days, or even weeks, the insoluble remains of the minute animals may be found inside the trap. [Illustration: FIG. 30. _Aldrovandia_: its trap apparatus. _A_, open. _St_, stalk of the leaf. _Spr_, blade of the leaf. _Stch_, sensitive bristles. _Dr_, glands. _B_, closed, a cross-section.] Many more cases of animal-catching plants might be adduced, but it is far from my intention to try to describe all the existing contrivances; those already mentioned may suffice to give an idea of the diversity and of the detailed effectiveness of these adaptations. They amplify--so it seems to me--our conception of the scope of natural selection, by showing us that adaptations may arise which are quite foreign to the original mode of life of the organism in question, and stand, indeed, in apparent contradiction to its fundamental physiological processes. It is hardly necessary to enter into a special argument to show that they can only have been brought about in the course of natural selection, since every other interpretation of their occurrence fails. Neither climatic nor any other external direct influence could have effected these modifications of the parts of plants, which are all so different, yet all so well suited to their purpose; they are different even in plants growing quite close together, like the sundew and the butterwort. The Lamarckian principle of use and disuse hardly enters into the question at all, since plants do not possess a will, and we can hardly speak of 'chance' where we have to do with such complex and diversely combined transformations. A process of selection actually operative in each of these cases can easily be thought out, and I shall leave it to my readers themselves to do this, and shall only indicate that we have to do with increasing