Thereupon we
become suspicious: we begin to wonder if the emergence from the
cocoon, that is to say, the hatching, really takes place in the order of
primogeniture. Might it not be--by a very singular exception, it is true,
but one which is necessary in such circumstances--that the youngest of
the Osmiae bursts her cocoon first and the oldest last; in short, that the
hatching proceeds from one chamber to the next in the inverse direction
to that which the age of the occupants would lead us to presume? In
that case, the whole difficulty would be removed: each Osmia, as she
rent her silken prison, would find a clear road in front of her, the
Osmiae nearer the outlet having gone out before her. But is this really
how things happen? Our theories very often do not agree with the
insect's practice; even where our reasoning seems most logical, we
should be more prudent to see what happens before venturing on any
positive statements. Leon Dufour was not so prudent when he, the first
in the field, took this little problem in hand. He describes to us the
habits of an Odynerus (Odynerus rubicola, DUF.) who piles up clay
cells in the shaft of a dry bramble-stalk; and, full of enthusiasm for his
industrious Wasp, he goes on to say:
'Picture a string of eight cement shells, placed end to end and closely
wedged inside a wooden sheath. The lowest was undeniably made first
and consequently contains the first-laid egg, which, according to rules,
should give birth to the first winged insect. How do you imagine that
the larva in that first shell was bidden to waive its right of
primogeniture and only to complete its metamorphosis after all its
juniors? What are the conditions brought into play to produce a result
apparently so contrary to the laws of nature? Humble yourself in the
presence of the reality and confess your ignorance, rather than attempt
to hide your embarrassment under vain explanations!
'If the first egg laid by the busy mother were destined to be the
first-born of the Odyneri, that one, in order to see the light immediately
after achieving wings, would have had the option either of breaking
through the double walls of his prison or of perforating, from bottom to
top, the seven shells ahead of him, in order to emerge through the
truncate end of the bramble-stem. Now nature, while refusing any way
of escape laterally, was also bound to veto any direct invasion, the
brutal gimlet-work which would inevitably have sacrificed seven
members of one family for the safety of an only son. Nature is as
ingenious in design as she is fertile in resource, and she must have
foreseen and forestalled every difficulty. She decided that the last-built
cradle should yield the first-born child; that this one should clear the
road for his next oldest brother, the second for the third and so on. And
this is the order in which the birth of our Odyneri of the Brambles
actually takes place.'
Yes, my revered master, I will admit without hesitation that the
bramble-dwellers leave their sheath in the converse order to that of
their ages: the youngest first, the oldest last; if not invariably, at least
very often. But does the hatching, by which I mean the emergence from
the cocoon, take place in the same order? Does the evolution of the
elder wait upon that of the younger, so that each may give those who
would bar his passage time to effect their deliverance and to leave the
road clear? I very much fear that logic has carried your deductions
beyond the bounds of reality. Rationally speaking, my dear sir, nothing
could be more accurate than your inferences; and yet we must forgo the
theory of the strange inversion which you suggest. None of the
Bramble-bees with whom I have experimented behaves after that
fashion. I know nothing personal about Odynerus rubicola, who
appears to be a stranger in my district; but, as the method of leaving
must be almost the same when the habitation is exactly similar, it is
enough, I think, to experiment with some of the bramble-dwellers in
order to learn the history of the rest.
My studies will, by preference, bear upon the Three-pronged Osmia,
who lends herself more readily to laboratory experiments, both because
she is stronger and because the same stalk will contain a goodly
number of her cells. The first fact to be ascertained is the order of
hatching. I take a glass tube, closed at one end, open at the other and of
a diameter similar to that of the Osmia's tunnel. In this I place, one
above the other, exactly in their natural order, the ten cocoons, or
thereabouts, which I extract from a
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