Un relevo generacional en la historia natural española. La Gasca y Graells: del científico liberal al naturalista isabelino

This article analyzes the Mariano de la Paz Graells' education in Barcelone, before he held the chair of zoology at the Natural History Museum in Madrid. Furthermore, some unpublished letters exchanged between Graells and Mariano La Gasca, his mentor, are studied. The subjet of the correspondence is nepotism.