"The Hunting Wasps": chapters 4 to 10 et passim.--Translator's Note.) The
outer envelope, consisting of pure silk, is thin, flexible and offers
little resistance. It is closely superimposed upon the inner envelope and
is easily separated from it everywhere, except at the anal end, where it
adheres to the second envelope. The adhesion of the two wrappers at one end
and the non-adhesion at the other are the cause of the differences which
the tweezers reveal when pinching the two ends of the cocoon.

The inner envelope is firm, elastic, rigid and, to a certain point,
brittle. I do not hesitate to look upon it as consisting of a silken tissue
which the larva, towards the end of its task, has steeped thoroughly in a
sort of varnish prepared not by the silk-glands but by the stomach. The
cocoons of the Sphex have already shown us a similar varnish. This product
of the chylific ventricle is chestnut-brown. It is this which, saturating
the thickness of the tissue, effaces the bright red of the beginning and
replaces it by a brown tint. It is this again which, disgorged more
profusely at the lower end of the cocoon, glues the two wrappers together
at that point.

The perfect insect is hatched at the beginning of July. The emergence takes
place without any violent effraction, without any ragged rents. A clean,
circular fissure appears at some distance from the top; and the cephalic
end is detached all of a piece, as a loose lid might be. It is as though
the recluse had only to raise a cover by butting it with her head, so exact
is the line of division, at least as regards the inner envelope, the
stronger and more important of the two. As for the outer wrapper, its lack
of resistance enables it to yield without difficulty when the other gives
way.

I cannot quite make out by what knack the Wasp contrives to detach the cap