The manner in which the snowy ribbon is formed also makes us reject the theory of different materials. We see the Mantis’ two caudal threads sweeping the surface of the foamy mass, skimming, so to speak, the top of the froth, collecting it and retaining it along the back of the nest to form a band that looks like a ribbon of icing. What remains after this sweeping, or what trickles from the band before it sets, spreads over the sides in a thin wash of bubbles so fine that they cannot be seen without the magnifying-glass. The surface of a muddy stream containing clay will be covered with coarse and dirty foam, churned up by the rushing torrent. On this foam, soiled with earthy materials, we see here and there masses of beautiful white froth, with smaller bubbles. Selection is due to the difference in density; and so the snow-white foam in places lies on top of the dirty foam whence it proceeds. Something similar happens when the Mantis builds her nest. The twin ladles reduce to foam the sticky spray from the glands. The thinnest and lightest portion, made whiter by its more delicate porousness, rises to the surface, where the caudal threads sweep it up and gather it into a snowy ribbon along the back of the nest. Until now, with a little patience, observation has been practicable and has given satisfactory results. It becomes impossible when we come to the very complex structure of that middle zone where exits are contrived for the emergence of the larvæ under the shelter of a double row of imbricated plates. The little that I am able to make out amounts to this: the tip of the abdomen, split wide from top to bottom, forms a sort of button-hole whose upper end remains almost fixed while the lower end, in swinging, produces foam and immerses eggs in it. It is that upper end which is undoubtedly responsible for the work of the middle zone. I always see it in the extension of that zone, in the midst of the fine white foam collected by the caudal filaments. These, one on the right, the other on the left, mark the boundaries of the band. They feel its edges; they seem to be testing the work. I can easily imagine them two long and exquisitely delicate fingers controlling the difficult business of construction. But how are the two rows of scales obtained and the fissures, the exit-doors, which they shelter? I do not know. I cannot even guess. I leave the rest of the problem to others.