Article révisé par les pairs
Résumé : Abstract. Fresh‐water sponges (Ephydatia fluviatilis) were cultivated in a mineral medium containing as little silica as technically possible (less than 15 μg/1). Some of their cells secreted an internal, slender, flexible rod. If, and only if, silica was added later to the medium, these rods were completed into spicules. It is suggested that these flexible rods correspond to the organic axes of normal spicules. This would mean that the differentiation of sclerocytes does not depend on the presence of usable concentrations of silica. Copyright © 1984, Wiley Blackwell. All rights reserved