It is perfectly evident, when we have the preparatory as well as the final condition of the wing before our eyes, that the wing-sheath of the larva is not a simple mould which elaborates the tissue enclosed in its own image and fashions the wing after the complexities of its own cavity. The future wing is not contained in the sheath as a bundle, which will astonish us, when expanded, by the extent and extreme complication of its surface. Or, to speak more exactly, it is there, but in a potential state. Before becoming an actual thing it is a virtual thing which is not yet, but is capable of becoming. It is there as the oak is inside the acorn. A fine transparent cushion limits the free edge of the embryo wing and the embryo wing-case. Under a powerful microscope we can perceive therein a few doubtful lineaments of the future lace-work. This might well be the factory in which life will shortly set its materials in movement. Nothing more is visible; nothing that will make us foresee the prodigious network in which each mesh must have its form and place predetermined with geometrical exactitude. In order that the organisable material can shape itself as a sheet of gauze and describe the inextricable labyrinth of the nervuration, there must be something better and more wonderful than a mould. There is a prototypical plan, an ideal pattern, which imposes a precise position upon each atom of the tissue. Before the material commences to circulate the configuration is already virtually traced, the courses of the plastic currents are already mapped out. The stones of our buildings co-ordinate according to the considered plan of the architect; they form an ideal assemblage before they exist as a concrete assemblage. Similarly, the wing of a cricket, that wonderful piece of lace-work emerging from a tiny sheath, speaks to us of another Architect, the author of the plans according to which life labours. The genesis of living creatures offers to our contemplation an infinity of wonders far greater than this matter of a locust's wing; but in general they pass unperceived, obscured as they are by the veil of time. Time, in the deliberation of mysteries, deprives us of the most astonishing of spectacles except our spirits be endowed with a tenacious patience. Here by exception the fact is accomplished with a swiftness that forces the attention. Whosoever would gain, without wearisome delays, a glimpse of the inconceivable dexterity with which the forces of life can labour, has only to consider the great locust of the vineyard. The insect will show him that which is hidden from our curiosity by extreme deliberation in the germinating seed, the opening leaf, and the budding flower. We cannot see the grass grow; but we can watch the growth of the locust's wings.