Abstract
Besides his work on marine biology which legacy is undisputed, Henri de LacazeDuthiers, as other 19th century zoologists, extended his interests to many fields of natural history. He was generally a keen observer (and very talented illustrator) of the anatomy of complex natural structures. In particular, he initiated studies on insect-induced galls addressed in his article "Recherches pour servir à l'histoire des galles" (Lacaze-Duthiers, 1853) and illustrated his research on the subject by magnificent drawings. The purpose of this essay is to report this lesser-known aspect of the work of H. de Lacaze-Duthiers. Without judging the value of Lacaze-Duthiers' research, we aim at extending the questions he raised at his time, and attempt to provide answers using recent knowledge on insect-induced gall diversity, ecology and physiology. In the process, we stress how the issues raised by Lacaze-Duthiers are connected to more general questions that apply to all biological associations between species (including parasitism). We will see that H. de Lacaze-Duthiers paper not only constitutes a pioneering work on insect galls but also addresses concepts that are still very relevant in current research, in particular on the genesis and development of galls.