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But the lobes, when soluble nitrogeneous matter is included, instead of remaining concave, thus containing within a concavity, slowly press closely together throughout their entire breadth, and as this takes place the margins gradually become a little everted, so that the spikes, which at first intercrossed, at last project in two parallel rows. So firmly do they become pressed together that, if any large insect has been caught, a corresponding projection is clearly visible on the outside of the leaf. When the two lobes are thus completely closed, they resist being opened, as by a thin wedge driven with astonishing force between them, and are generally ruptured rather than yield. If not ruptured, they close again with quite a loud flap. The slow movement spoken of, excited by the absorption of diffused animal matter, suffices for its final purpose, whilst the movement brought on by the touching of one of the sensitive filaments is rapid, and thus indispensable for the capturing of insects.