The eggs are set in a yellowish medium of horny appearance.  They are arranged in layers, in lines forming arcs of a circle, with the cephalic extremities converging towards the zone of issue.  This orientation tells us of the method of delivery.  The newly-born larvae will slip into the interval between two adjacent flaps or leaves, which form a prolongation of the core; they will then find a narrow passage, none too easy to effect, but sufficient, having regard to the curious provision which we shall deal with directly; they will then reach the zone of issue.  There, under the overlapping scales, two passages of exit open for each layer of eggs.  Half the larvae will issue by the right-hand passage, half by that on the left hand.  This process is repeated for each layer, from end to end of the nest.

Let us sum up those structural details, which are not easily grasped unless one has the nest before one.  Lying along the axis of the nest, and in shape like a date-stone, is the mass of eggs, grouped in layers.  A protective rind, a kind of solidified foam, envelops this core, except at the top, along the central line, where the porous rind is replaced by thin overlapping leaves.  The free edges of these leaves form the exterior of the zone of issue; they overlap one another, forming two series of scales, leaving two exits, in the shape of narrow crevices, for each layer of eggs.

[Illustration:  1.  NEST OF THE PRAYING MANTIS.

2.  TRANSVERSE SECTION OF THE SAME.

3, 3a.  NEST OF EMPUSA PAUPERATA.

4.  TRANSVERSE SECTION OF THE SAME.

5.  VERTICAL SELECTION OF THE SAME.

6.  NEST OF THE GREY MANTIS.

7.  SCHEFFER’S SISYPHUS (see Chap.  XII.)

8.  PELLET OF THE SISYPHUS.

9.  PELLET OF THE SISYPHUS WITH DEJECTA OF THE LARVA FORCED THROUGH THE WALLS.]

To be present at the construction of the nest—­to learn how the Mantis contrives to build so complex a structure—­such was the main point of my researches.  I succeeded, not without difficulty, as the eggs are laid without warning and nearly always at night.  After a great deal of futile endeavour, chance at last favoured me.  On the 5th of September one of my guests, fecundated on the 29th of August, began to make her preparations under my eyes, at four o’clock in the afternoon.

One remark before proceeding:  all the nests I have obtained in the laboratory—­and I have obtained a good number—­have without exception been built upon the wire gauze of the covers.  I have been careful to provide the insects with roughened stones and tufts of thyme, both being very commonly used as foundations in the open fields.  The captives have always preferred the network of wire gauze, which affords a perfectly firm foundation, as the soft material of the nest becomes incrusted upon the meshes as it hardens.

In natural conditions the nests are never in any way sheltered; they support the inclemencies of winter, resist rain, wind, frost, and snow, without becoming detached.  It is true that the female always selects an uneven support on which the foundations of the nest can be shaped, thus obtaining a firm hold.  The site chosen is always the best obtainable within reach, and the wire gauze is constantly adopted as the best foundation obtainable in the cages.