Up on a high shelf, perhaps only for the eyes of those with the wherewithal to look, a desiccated human head screamed silently from within a bell jar, its teeth crusted with brown plaque. Hairless, nose mostly gone, the left side of the head was crept over by a dusty web, something fibrous. The head looked as if it would crumble to dust if the bell jar were to be lifted.

And there was more. In a back room, we discovered a gallery of wooden cabinets, their many drawers shallow and wide and easily pulled open to reveal trays of insects, perfectly preserved and held in place with fine metal pins. Butterflies of silvery blue and green, grasshoppers, termites, moths and dragonflies. Bees, wasps, scorpions and aphids. It was almost too much. Slick pincered beetles covered in intricate armour, dried larvae husks, a hairy tarantula bigger than my fist.

Looping her arm around mine, Axelle said something peculiar about female spiders.

‘Pardon?’ I said, turning to her. I had been distracted by a cabinet that displayed a series of ammonite fossils; small, shiny coils of ancient sea creatures, embedded in rough ears of rock. But then Axelle’s arm twisted with mine, and I quickly forgot about the fossils.

‘There is a type of female spider,’ she said. ‘She kills her male companions after the act of mating.’

‘C’est vrai?’

‘Yes. I think they eat them too.’

‘How awful.’

We carried on to the back of the room where a small man sat at a worktable, his left eye greatly magnified by a round glass strapped to his head. He was bent over his work, arranging the iridescent wings of a giant butterfly, lost in this task.

Axelle pulled me to lean against the wall and put her mouth to my ear. ‘He lives with his mother,’ she whispered. ‘He’s been obsessed with insects since he was a boy. He used to collect spiders from under his bed and would keep them in clay jars, feeding them house flies and ants. But they always died.’ She looked at me, her shoulders shaking with silent laughter. ‘He’s been in love once but she wouldn’t marry him. Too many dead moths and crickets in jars.’

I played along. ‘His father wanted him to train to do something clerical. Something sensible with money, with numbers.’

‘His father ran off with another woman. Mademoiselle Scarabée.’ Axelle snorted, slapped her hand over her mouth.

The poor man looked at us, one eyebrow arched, his left eye swimming behind glass.

We left Deyrolle’s feeling very wicked, and as I still had some time before Madame expected me home, and as the weather was lovely and mild, we decided to walk along the river. I didn’t want to say goodbye yet, nor, I thought, did she. Crossing under the Pont Alexandre III, we stopped to watch a group of titis scampering over the iron girders like a pack of squirrels in the trees. Under the young boys’ feet, the Seine flowed, and the September light that shone through the iron struts and arches penetrated the water, and the water was green and inviting.