Structure of shells from eggs of the geckos Gekko gecko and Phelsuma madagascarensis

The geckos Gekko gecko and Phelsuma madagascarensis lay small, round eggs with brittle, inflexible shells. Eggshells of both species consist of a thick calcareous layer with an organic layer adhering to the outer surface and a thin, fibrous shell membrane attached to the inner surface. The calcareous layer consists of calcium carbonate in the form of calcite, and is organized into ill-defined columns that form a dense crystalline matrix. The inner face of columns (the aspect attached to the shell membrane) consists of crystallites of variable size and morphology. Eggshells contain a great deal of organic matter, and prolonged treatment with NaOH leaves the calcareous layer riddled with horizontal fissures reflecting the removal of organic matrix. Pores through the calcareous layer of eggshells of both species terminate at the outer surface in a variable number of small openings. The pore canal in G. gecko eggshells occurs as a series of labyrinthine channels in a calcareous concretion that fits loosely within a corresponding cleft in the calcareous layer. Detachment of the concretion leaves a shallow pit or depression on the inner surface of the eggshell. We observed concretions and pits in P. madagascarensis eggshells but were unable to characterize the nature of the pore canal in this species.