Ostrich and hen eggs were subjected to a microstructural comparison of the shell and shell membrane in the raw condition and of the albumen and yolk in the hard-boiled condition. The observation methods used were optical microscopy, scanning electron microscopy and low-vacuum scanning electron microscopy. The ostrich eggshell had a finely crackled surface. The structural components of the transverse section of the ostrich eggshell were similar to those of the hen eggshell. The shell and its vertical crystal layer of the ostrich egg were approximately five times thicker than those of the hen egg, and the spongy matrix region occupied three-quarters of the thickness of the ostrich eggshell. The results suggest that these factors were involved in the hardness of the ostrich eggshell. The ostrich eggshell membrane was two-to three-fold the thickness of the hen eggshell membrane, being composed of thick twisted fibers. The intermediate layer of the ostrich albumen showed a fine-layered structure, which seemed to be composed of thick albumen. The inner layer of the ostrich albumen comprised about 40% of the whole thickness, although its structure was indeterminate. The intensity of staining of the inner and outer layers of the ostrich albumen by the PAS reaction was stronger than that for the hen egg albumen. The ostrich yolk was packed with polyhedral yolk spheres, these yolk spheres having a similar shape and size to those of the hen yolk.
