Histologie du pancreas. In Traité d'anatomie humaine, edited by Paul Julien Poirier & Adrien Charpy, vol. 4, pp. 821-831.

Laguesse, who in 1893 named the islets of Langerhans, established in this work that the islets of Langerhans were the seat of internal secretion of the pancreas. On figures 425 and 427 he drew that are now called "the beta cells of the islets of Langerhans."

(Thanks to Juan Weiss for this reference and its interpretation.)