_dn._ Modified nucleus of primitive ovum. _do._ Permanent ovum in the act of being formed. _dv._ Developing blood-vessels. _dyk._ Developing yolk. _ep._ Non-ovarian epithelium of ovarian ridge. _fe._ Follicular epithelium. _gv._ Germinal vesicle. _lstr._ Lymphatic region of stroma. _n n._ Nests of nuclei of ovarian region. _o._ Permanent ovum. _ovr._ Ovarian portion of ovarian ridge. _po._ Primitive ovum. _ps e._ Pseudo-epithelium of ovarian ridge. _str._ Stroma ingrowths into ovarian epithelium. _v._ Blood-vessel. _vstr._ Vascular region of stroma adjoining ovarian ridge. _vt._ Vitelline membrane. _x._ Modified nucleus. _yk._ Yolk. _zn._ Zona radiata. Fig. 1. Transverse section of the ovarian ridge of an embryo of _Scy. canicula_, belonging to stage P, shewing the ovarian region with thickened epithelium and numerous primitive ova. Zeiss C, ocul. 2. _Picric acid._ Fig. 2. Transverse section of the ovarian ridge of an embryo of _Scyllium canicula_, considerably older than stage Q. Zeiss C, ocul. 2. _Picric acid._ Several nests, some with distinct ova, and others with the ova fused together, are present in the section (_nn_), and several examples of modified nuclei in still distinct ova are also represented. One of these is marked _x_. The stroma of the ovarian ridge is exceptionally scanty. Fig. 3. Transverse section through part of the ovarian ridge, including the ovarian region of an almost ripe embryo of _Scyllium canicula_. Zeiss C, ocul. 2. _Picric acid._ Nuclear nests (_n.n._), developing ova (_d.o._), and ova (_o._), with completely formed follicular epithelium, are now present. The ovarian region is still well separated from the subjacent stroma, and does not appear to contain any cells except those of the original germinal epithelium. Fig. 4. Section through ovarian ridge of the same embryo as fig. 3, to illustrate the relation of the stroma (_str._) and ovarian region. Zeiss _a a_, ocul. 2. _Picric acid._ Fig. 5. Section through the ovarian ridge of an embryo of _Scyllium canicula_, 10 cm. long, in which the ovary was slightly less advanced than in fig. 3. To illustrate the relation of the ovarian epithelium to the subjacent vascular stroma. Zeiss A, ocul. 2. _Osmic acid._ _y._ points to a small separated portion of the germinal epithelium. Fig. 6. Section through the ovarian ridge of an embryo of _Scyllium canicula_, slightly older than fig. 5. To illustrate the relation of the ovarian epithelium to the subjacent vascular stroma. Zeiss A, ocul. 2. _Osmic acid._ Fig. 7. More highly magnified portion of the same ovary as fig. 6. To illustrate the same points. Zeiss C, ocul. 2. _Osmic acid._ Fig. 8. Section through the ovarian region (close to one extremity, where it is very small) from a young female of _Scy. canicula_. Zeiss C, ocul. 2. _Picric acid._ It shews the vascular ingrowths amongst the original epithelial cells of the ovarian region.