At the end of 17th century, another invention changed the course of watchmaking: the balance spring, which helps regulate the mechanism and improve timekeeping accuracy. “Watches could keep time within minutes per day,” Mr. Bull said. “Everyone was taken with having a watch that could be used to tell time and set your day by. Form watches continued to appear, in the shape of a parrot, a turkey, a chimera or fantastic bird, rabbits, dolphins, dogs, lions, tulips, sea urchins, doves and others.”

Miranda Marraccini, the librarian at the Horological Society of New York, wrote in an email that improvements in enameling and engraving techniques at the end of the 18th century and beginning of the 19th “allowed artisans to create very realistic and detailed watches in the shape of fruit, animals and objects like hats and baskets. Many watches also drew connections to other preoccupations of the period — hot air balloons, for instance.”

“My favorite form watch,” she wrote, “is a little pistol from the early 1800s. It’s only a few inches long and covered in pearls and enamel. It has a secret compartment in the handle that opens to reveal a tiny watch dial. Pulling the trigger releases a red enameled flower bud from the end of the pistol, which in turn squirts perfume from its center.”

Technological developments beyond watchmaking affected form watches, too. “From 1850, you get another change,” Mr. Bull said, “the introduction of the railways. Time is important. Toys were not so interesting to people as watches that kept the best possible timekeeping.”

“There are not many surviving watches from the 1850s onward that you could call true form watches,” he said. “The next time they appear, from 1900 onwards, is effectively as jewelry,” such as Bulgari’s Serpenti.

To Luc Van Cauwenbergh, a watch collector in Brussels, “form watches are pieces of art and witness the unlimited creativity of the goldsmiths in shape and decoration.”