What purpose the marginal spikes, which form so conspicuous a feature in the appearance of the plant, subserve was unknown until the genius of Darwin solved the mystery. It was he that showed that elongated spaces between the spikes, varying from one-fifteenth to one-tenth of an inch in breadth according to the size of the leaf, are left open for a short time before the edges of the lobes come into contact, consequent upon the intercrossing of the tips of the marginal spikes first, thus enabling an insect whose body is not thicker than these measurements to escape, when disturbed by the closing lobes and the increasing darkness, quite easily between the crossed spikes. Moderately sized insects, if they try to escape between the bars, will be pushed back into the horrid prison with the slowly closing walls, for the spikes continue to close more and more until the lobes are brought into contact. Very strong insects, however, manage to effect their release. It would manifestly be a great disadvantage to the plant to remain many days clasped over a minute insect, and as many additional days or weeks in recovering its sensibility, inasmuch as a very small insect would afford but little nourishment. Far better would it be for the plant to wait until a moderately large insect was captured, and to allow the little ones to escape, and this advantage is gained by the slow intercrossing of the marginal spikes, which, acting like the large meshes of a fishing-net, allow the small and worthless fry to pass through.