Ultrastructure of the calcareous layer eggshell of the turtle Emys orbicularis (L.). Preliminary study.

The calcareous layer of Emys orbicularis eggshell was examined by scanning electron microscopy. The layer is composed of well distinguished shell units which consist of needle-like crystallites radiating outwards from the cores. The linear structures of the cores on the inner surface appear to be similar to those in the eggshell of Mauremys caspica. On the inner surface of shell units of eggs with dead embryos there are flat, conical depressions. This surface in specimens from unfertilized eggs is almost flat. It may suggest that a developing embryo derives calcium from the eggshell.