Hydra's Heads and Medusa's Blood 37
ence's capacity for self-delusion. Even Reaumur, when he failed to find
tiny butterfly wings inside caterpillars, assumed they were there but
were too small to be seen. Only a few months before Trembley began
slicing hydras, his cousin, Genevan naturalist Charles Bonnet, had
proven (in an experiment suggested by the omnipresent Reaumur) that
female aphids usually reproduced parthenogenetically (without mating).
To Bonnet this demonstrated that the tiny adult resided in the egg, and
he became the leader of the ovist preformationists.
The hydra's regeneration, and similar powers in starfish, sea ane-
mones, and worms, put the scientific establishment on the defensive.
Reaumur had long ago realized that preformation couldn't explain how a
baby inherited traits from both father and mother. The notion of two
homunculi fusing into one seed seemed farfetched. His regrowing
crayfish claws showed that each leg would have to contain little pre-
formed legs scattered throughout. And since a regenerated leg could be
lost and replaced many times, the proto-legs would have to be very
numerous, yet no one had ever found any.
Regeneration therefore suggested some form of epigenesis—perhaps
without a soul, however, for the hydra's anima, if it existed, was divisi-
ble along with the body and indistinguishable from it. It seemed as
though some forms of matter itself possessed the spark of life. For lack of
knowledge of cells, let alone chromosomes and genes, the epigeneticists
were unable to prove their case. Each side could only point out the
other's inconsistencies, and politics gave preformationism the edge.
No wonder nonscientists often grew impatient of the whole argu-
ment. Oliver Goldsmith and Tobias Smollett mocked the naturalists for
missing nature's grandeur in their myopic fascination with "muck-flies."
Henry Fielding lampooned the discussion in a skit about the regenera-
tion of money. Diderot thought of hydras as composite animals, like
swarms of bees, in which each particle had a vital spark of its own, and
lightheartedly suggested there might be "human polyps" on Jupiter and
Saturn. Voltaire was derisively skeptical of attempts to infer the nature
of the soul, animal or human, from these experiments. Referring in
1768 to the regenerating heads of snails, he asked, "What happens to its
sensorium, its memory, its store of ideas, its soul, when its head has
been cut off? How does all this come back? A soul that is reborn is an
extremely curious phenomenon." Profoundly disturbed by the whole af-
fair, for a long time he simply refused to believe in animal regeneration,
calling the hydra " a kind of small rush."
It was no longer possible to doubt the discovery after the work of
Lazzaro Spallanzani, an italian priest for whom science was a full-time