Fig. 9. Section through the ovarian region of the same embryo as fig. 8, at its point of maximum development. Zeiss A, ocul. 2. _Picric acid._ Fig. 10. Section through superficial part of the ovary of an embryo, shewing the pseudo-epithelium; the cells of which are provided with tails prolonged into the general tissue of the ovary. At _f.e._ is seen a surface view of the follicular epithelium of an ovum. Zeiss C, ocul. 2. _Picric acid._ Fig. 11. Section through part of an ovary of _Scyllium canicula_ of stage Q, with three primitive ova, the most superficial one containing a modified nucleus. Fig. 12. Section through part of an ovary of an example of _Scyllium canicula_, 8 cm. long. The section passes through a nest of ova with modified nuclei, in which the outlines of the individual ova are quite distinct. Zeiss E, ocul. 2. _Picric acid._ Fig. 13. Section through part of ovary of the same embryo as in fig. 5. The section passes through a nest of nuclei, with at the least two developing ova, and also through one already formed permanent ovum. Zeiss E, ocul. 2. _Osmic acid._ Figs. 14, 15, 16, 17, 18 [Figs. 17 and 18 are on Pl. 25]. Sections through parts of the ovary of the same embryo as fig. 3, with nests of nuclei and a permanent ova in the act of formation. Fig. 14 is drawn with Zeiss D D, ocul. 2. Figs. 15, 16, 17, with Zeiss E, ocul. 2. _Picric acid._ PLATE 25. LIST OF REFERENCE LETTERS. _do._ Permanent ovum in the act of being formed. _dyk._ Developing yolk. _fe._ Follicular epithelium. _fe´._ Secondary follicular epithelium. _gv._ Germinal vesicle. _nn._ Nests of nuclei of ovarian region. _o._ Permanent ovum. _pse._ Pseudo-epithelium. _str._ Stroma ingrowths into ovarian epithelium. _vt._ Vitelline membrane. _x._ Modified nucleus. _yk._ Yolk (vitellus). _zn._ Zona radiata. [Figs. 17 and 18. Vide description of Plate 24.] Fig. 19. Two nuclei from a nest which appear to be in the act of division. From ovary of the same embryo as fig. 3. Fig. 20. Section through part of an ovary of the same embryo as fig. 6, containing a nest of nuclei. Zeiss F, ocul. 2. _Osmic acid._ Fig. 21. Ovum from the ovary of a half-grown female, containing isolated deeply stained patches of developing yolk granules. Zeiss B, ocul. 2. _Picric acid._ Fig. 22. Section through a small part of the ovum of an immature female of _Scyllium canicula_, to shew the constitution of the yolk, the follicular epithelium, and the egg membranes. Zeiss E, ocul. 2. _Chromic acid._ Fig. 23. Section through part of the periphery of a nearly ripe ovum of _Scy. canicula_. Zeiss C, ocul. 2. It shews the remnant of the vitelline membrane (_v.t._) separating the columnar but delicate cells of the follicular epithelium (_f.e._) from the yolk (_yk._). In the yolk are seen yolk-spherules in a protoplasmic network. The transverse markings in the yolk-spherules have been made oblique by the artist.