Étude ultrastructurale de la fécondation chez Grantia compressa F.

The fertilization of a calcareous sponge is studied by means of the electron microscope, in Grantia compressa F.. The mature oocyte lies beneath the choanoderm; the carrier cell is applied to its surface, and the spermiocyst enters its cytoplasm. The ultrastructural study demonstrates two formations in this spermiocyst: (i) the ‘head’, surrounded by a lamellar envelope, consists mainly of a nucleus with ring-shaped chromatin; (ii) a large area with a periodic structure corresponding to the modified ‘middle piece’ or ‘mitochondrial body’ of other authors.