The structure of the eggshell and eggshell membranes of Crocodylus niloticus.

The macro- and microstructure, elemental composition, and crystallographic characteristics of the eggshell and eggshell membranes of the Crocodylus niloticus egg was investigated using optical and electron microscopy, energy-dispersive X-ray spectroscopy (EDS), electron back scatter diffraction (EBSD) and computerized tomography. The translucent ellipsoid egg is composed of two basic layers, the outer calcified layer referred to as the shell and an inner organic fiber layer, referred to as the shell membrane. The outer inorganic calcite shell is further divided into an external, palisade and mammillary layers with pore channels traversing the shell. The external layer is a thin layer of amorphous calcium and phosphorus, the underlying palisade layer consist of irregular wedge-shaped crystals composed calcite with traces of magnesium, sodium, sulphur, and phosphorus. The crystals are mostly elongated, orientated perpendicular to the shell surface ending in cone shaped knobs which forms the inner mammillary layer. The elemental composition of the mammillae is like that of the palisade layer, but the crystal structure is much smaller and orientated randomly. The highest number of mammillae and shell pores are found at the equator of the egg, becoming fewer towards the egg poles. The shell thickness follows the same pattern, with the thickest area located at the equator. The eggshell membrane located right beneath and embedded in the mammillary layer of the shell; it is made up of unorganized fiber sheets roughly orientated at right angles to one another. Individual fibers consist of numerous smaller fibrils forming open channels that runs longitudinally through the fiber. The basic measurements, and microscopic and chemical structure of the Nile crocodile egg was studied using several microscopy and analytical techniques. It was found that the translucent white egg has two basic layers; the outer shell and inner membrane. The outer shell is further divided into three layers and has openings, called pores extending between the inside and outside of the shell. The highest number of the pores is found around the middle circumference of the egg. The outermost layer is a thin characterless layer made up of calcium and phosphorus, and the middle layer consists of interlocking wedge-shaped calcite crystals with traces of magnesium, sodium, sulphur, and phosphorus. These crystals end in cone shaped knobs on the inner aspect of the shell and then also forms the third inner layer of the shell. The amount of these knobs, called mammillae, are highest at the equator of the egg and becomes fewer towards the egg poles. The shell thickness follows the same pattern, with the thickest area located at the equator. The second layer of the egg, the membrane is found right beneath the shell and is embedded in the mammillae. The membrane is composed of numerous fibers roughly arranged in parallel sheets of varying directions. Each individual fiber is made up of smaller fibrils clustered together, and forming open channels that runs lengthwise through the fiber. This article is protected by copyright. All rights reserved.