Moreover, the method by which the snowy band is formed rejects the idea of a different material.  We see the two caudal appendices of the Mantis sweeping the surface of the foamy mass, and skimming, so to speak, the cream of the cream, gathering it together, and retaining it along the hump of the nest in such a way as to form a band like a ribbon of icing.  What remains after this scouring process, or what oozes from the band before it has set, spreads over the sides of the nest in a thin layer of bubbles so fine that they cannot be distinguished without the aid of a lens.

We often see a torrent of muddy water, full of clay in suspension, covered with great streaks and masses of foam.  On this fundamental foam, so to call it, which is soiled with earthy matters, we see here and there masses of a beautiful white foam, in which the bubbles are much smaller.  A process of selection results from variations in density, and here and there we see foam white as snow resting on the dirty foam from which it is produced.  Something of the kind occurs when the Mantis builds her nest.  The two appendices whip the viscous secretion of the glands into foam.  The lightest portion, whose bubbles are of the greatest tenuity, which is white on account of its finer porosity, rises to the surface, where the caudal filaments sweep it up and gather it into the snowy ribbon which runs along the summit of the nest.

So far, with a little patience, observation is possible and yields a satisfactory result.  It becomes impossible in the matter of the complex central zone, where the exits for the larvae are contrived through the double series of overlapping leaves.  The little I have been able to learn amounts to this:  The end of the abdomen, deeply cleft in a horizontal direction, forms a kind of fork, of which the upper extremity remains almost motionless, while the lower continuously oscillates, producing the foam and depositing the eggs.  The creation of the central zone is certainly the work of the upper extremity.

It is always to be seen in the continuation of this central zone, in the midst of the fine white foam gathered up by the caudal filaments.  The latter delimit the zone, one working on either side, feeling the edges of the belt, and apparently testing it and judging its progress.  These two filaments are like two long fingers of exquisite sensitiveness, which direct the difficult operation.

But how are the two series of scales obtained, and the fissures, the gates of exit which they shelter?  I do not know; I cannot even imagine.  I leave the end of the problem to others.