PETTER, an ingenious naturalist, descended from an ancient family of Lorraine, was born at Maestricht in 1707. At school he showed a singular aptitude for languages, and in a short time became an adept in Latin, Greek, Hebrew, French, Italian, Spanish, German, and English. His father, a minister of the French church at Heusden, had designed him for a clergyman, and accordingly with that view Lyonnet entered the university of Leyden. There, in addition to the prescribed subjects, he studied anatomy, music, drawing, and sculpture. Abandoning all intention of entering the church, he soon afterwards applied himself to law; and after he had graduated at Utrecht, practised for some time at the Hague. He then began to study deciphering, and in a short time was appointed secretary of ciphers and translator of Latin and French to the states-general of the United Provinces. The time not engrossed by these offices was employed by Lyonnet in amassing materials and executing plates for a description which he intended to write of the insects found in the vicinity of the Hague. Abandoning this project, however, he contented himself with contributing some of his materials to a French translation of Lesser's work on This translation, along with Lyonnet's remarks, was reprinted at Paris in 1745, by the celebrated Reaumur. Meanwhile, in 1744, he had designed and engraved the plates for Trembley's work on the fresh-water polypus. He was chosen a fellow of the Royal Society of London in 1748, and a member of the Society of Sciences at Haarlem in 1753. In 1757 he was elected a member of the Royal Academy of Sciences at Rome, through the influence of the celebrated M. Le Cat, its perpetual secretary. The publication in 1760 of his chief work, *Traité Anatomique de la Chenille qui rouge le bois de Saule*, spread his reputation, and he was honoured with diplomas of membership from the Royal Academy of Sciences of Berlin in 1760, from the Imperial Academy of Naturalists in 1761, and from the Imperial Academy of Sciences at St Petersburg in 1762. A description and plate of the instruments he had used in dissecting the chenille were published by Lyonnet in the *Transactions* of the Society of Sciences at Haarlem, and afterwards in French at the beginning of his *Traité Anatomique*. He had intended to pursue this track of inquiry, and to examine the animal above named in its various stages of development; but at the age of sixty an accident impaired his eyesight, and thus defeated his cherished plan. The last fifteen or twenty years of his life were spent in adding to his valuable collection of horns and shells a choice cabinet of more than 560 paintings. Lyonnet died at the Hague in 1789.