The basal lamina of epithelia in vertebrates appears homogeneous, but in invertebrates it occasionally shows periodic density differences in cross section. This electron micrograph of the base of a cell in the gut epithelium of a flea, inset is a horizontal section of the same, illustrates this phenomenon. When sectioned parallel to the base of the epithelium (inset at lower left), it appears as a mosaic of elongated dense bodies separated by rows of smaller dense granules. Micrograph courtesy of Susumu Ito.