which I cannot easily break up with my pick. Although similar
facts abound in insect history, we always notice them with a lively
interest. They tell us of an incomprehensible power which suddenly, at
a given moment, irresistibly commands an obscure grub to abandon the
retreat in which it enjoys security, in order to make its way through
a thousand difficulties and to reach the light, which would be fatal
to it on any other occasion, but which is necessary to the perfect
insect, which could not reach it by its own efforts.

But the layer of Osmia-cells has been removed; and the pick now
reaches the Anthophora's cells. Among these cells are some which
contain larvae and which result from the labours of last May; others,
though of the same date, are already occupied by the perfect insect.
The precocity of metamorphosis varies from one larva to another;
however, a few days' difference of age is enough to explain these
inequalities of development. Other cells, as numerous as the first,
contain a parasitical Hymenopteron, a Melecta (_M. armata_), likewise
in the perfect state. Lastly, there are some, indeed many, which
contain a singular egg-shaped shell, divided into segments with
projecting breathing-pores. This shell is extremely thin and fragile;
it is amber-coloured and so transparent that one can distinguish quite
plainly, through its sides, an adult Sitaris (_S. humeralis_), who
occupies the interior and is struggling as though to set herself at
liberty. This explains the presence here, the pairing and the
egg-laying of the Sitares whom we but now saw roaming, in the company
of the Anthrax-flies, at the entrance to the galleries of the
Anthophorae. The Osmia and the Anthophora, the joint owners of the
premises, have each their parasite: the Anthrax attacks the Osmia and
the Sitaris the Anthophora.

But what is this curious shell in which the Sitaris is invariably
enclosed, a shell unexampled in the Beetle order? Can this be a case
of parasitism in the second degree, that is, can the Sitaris be living
inside the chrysalis of a first parasite, which itself exists at the
cost of the Anthophora's larva or of its provisions? And, even so, how
can this parasite, or these parasites, obtain access to a cell which
seems to be inviolable, because of the depth at which it lies, and
which, moreover, does not reveal, to the most careful examination
under the magnifying-glass, any violent inroad on the enemy's part?
These are the