Louis Sébastien Tredern de Lézérec (1780-18?), a forgotten pioneer of chick embryology

Tredern's thesis on chick embryo development was submitted in Jena (Germany) in 1808 and seems to have been completely overlooked by historians of embryology during the 20th century. However, K.E. von Baer and C. Pander were much interested in that thesis in 1816-1817, when they resumed work on the chick embryo. Tredern, who was born in France in 1780, had then left Germany and abandoned his studies, but von Baer tried to find trace of him throughout his life, wanting to pay homage to his pioneer work. Von Baer published a short biographical notice (1874), which was later extended by Stieda (1901). The accuracy of Tredern's observations and the reasons that could have justified von Baer's interest are discussed. Tredern went back to Paris in 1811 to submit a second medical thesis, the value of which is also considered. It is also shown that, in the teaching of embryology, 18th century preformation concepts were still vivid, remaining in French textbooks of the period 1800-1830. This situation strongly contrasts with the new epigenetic views that were developed by the German scientists with whom Tredern had performed his studies.