o the tin and lay the eggs inside, on the very edges of
the slit. Whether outside or in, the eggs are dabbed down in a fairly
regular and absolutely white layer. I as it were shovel them up with a
little paper scoop. I thus obtain all the germs that I require for
my experiments, eggs bearing no trace of the stains which would be
inevitable if I had to collect them on tainted meat.

We have seen the bluebottle refusing to lay her eggs on the paper bag,
notwithstanding the carrion fumes of the Linnet enclosed; yet now,
without hesitation, she lays them on a sheet of metal. Can the nature of
the floor make any difference to her? I replace the tin lid by a paper
cover stretched and pasted over the orifice. With the point of my knife,
I make a narrow slit in this new lid. That is quite enough: the parent
accepts the paper.

What determined her, therefore, is not simply the smell, which can
easily be perceived even through the uncut paper, but, above all, the
crevice, which will provide an entrance for the vermin, hatched outside,
near the narrow passage. The maggots' mother has her own logic, her
prudent foresight. She knows how feeble her wee grubs will be, how
powerless to cut their way through an obstacle of any resistance; and
so, despite the temptation of the smell, she refrains from laying so
long as she finds no entrance through which the newborn worms can slip
unaided.

I wanted to know whether the color, the shininess, the degree of
hardness and other qualities of the obstacle would influence the
decision of a mother obliged to lay her eggs under exceptional
conditions. With this object in view, I employed small jars, each baited
with a bit of butcher's meat. The respective lids were made of different
colored paper, of oilskin, or of some of that tinfoil, with its gold or
coppery sheen, which is used for sealing liqueur bottles. On not one
of these covers did the mothers stop, with any desire to deposit their
eggs; but, from the moment that the knife had made the narrow slit,
all the lids were, sooner or later, visited and all of them, sooner or
later, received the white shower somewhere near the gash. The look of
the obstacle, therefore, does not count; dull or brilliant, drab or
colored: these are details of no importance; the thing that matters is
that there should be a passage to allow the grubs to enter.

Though hatched outside, at a distance from the coveted morsel, the
newborn worms are well able to find