In the sections of one of my embryos of this stage they are especially well shewn, and the following description is taken from those displayed in that embryo. They are confined to the region which extends posteriorly nearly to the end of the small intestine and anteriorly to the abdominal opening of the segmental duct. Their situation in this region is peculiar. There is no trace of a distinct genital ridge, but the ova mainly lie in the dorsal portion of the mesentery, and therefore in a part of the mesoblast which distinctly belongs to the splanchnopleure (Pl. 12, fig. 14_a_). Some are situated external to the segmental involutions; and others again, though this is not common, in a part of the mesoblast which distinctly belongs to the body-wall (Pl. 12, fig. 14_b_). The portion of mesentery, in which the primitive ova are most densely aggregated, corresponds to the future position of the genital ridge, but the other positions occupied by ova are quite outside this. Some ova are in fact situated on the outside of the segmental duct and segmented tubes, and must therefore effect a considerable migration before reaching their final positions in the genital ridge on the inner side of the segmental duct (Pl. 12, fig. 14_b_). The condition of the tissue in which the ova appear may at once be gathered from an examination of the figures given. It consists of an irregular epithelium of cells partly belonging to the somatopleure and partly to the splanchnopleure, but passing uninterruptedly from one layer to the other. The cells which compose it are irregular in shape, but frequently columnar (Pl. 12, figs. 14_a_ and 14_b_). They are formed of a nucleus which stains deeply, invested by a _very delicate_ layer of protoplasm. At the junction of somatopleure and splanchnopleure they are more rounded than elsewhere. Very few loose connective-tissue cells are present. The cells just described vary from .008 Mm. to .01 Mm. in diameter. The primitive ova are situated amongst them and stand out with extraordinary clearness, to which justice is hardly done in my figures. The normal full-sized ova exhibit the following structure. They consist of a mass of somewhat granular protoplasm of irregular, but more or less rounded, form. Their size varies from .016 - .036 Mm. In their interior a nucleus is present, which varies from .012 - .016 Mm., but its size as a rule bears _no_ relation to the size of the containing cell. This is illustrated by the subjoined list of measurements. Size of Primitive ova in Size of nucleus of Primitive degrees of micrometer scale ova in degrees of micrometer with F. ocul 2. scale with F. ocul 2.