PLATE 'HYll—Co^/iiHued. 



Fig. 9. — Section thro\i<i;h tlie ovarian region of the same embryo as fig. 8, 

 at its point of maximum development. Zeiss, a, ocul. 2. Picric acid. 



Fig. 10. — Section tluougli superficial part of the ovary of an embryo, 

 showing the pseudo-epithelium ; the cells of wliich are provided with tails 

 prolonged into the general tissue of the ovary. At / e. is seen a surface 

 view of the follicular epithelium of an ovum. Zeiss, c, ocul. 2. Picric acid. 



EXPLANATION OF PLATE XVIII. 



List of Reference Letters. 



0. Permanent ovum. do. Developing ovum, g v. Germinal vesicle. 

 fe. Follicular epithelium. 7/k. Yolk. d^i. Developing yolk. pL Vitel- 

 line membrane, en. Zona radiata. dn. Modified nucleus of primitive 

 ovum. pse. Pseud-epithelium of ovarian region sir. Stroma ingrowths 

 into ovarian epithelium. 



Fig. 11. — Section through part of an ovary of Sci/llium 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 Sci/llium 

 canicida, 8 c. m. long. The section passes through a nest of ova with 

 modified nuclei, in which the outlines of the individual ov-i are quite dis- 

 tinct. 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. — 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. 



Fig. 19. — Two nuclei from a nest which appear to be in the act of divi- 

 sion. 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. Osraic 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 Scvllium canicula, to show the constitution of the yolk, the folli- 

 cular 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 Sci/. canicula. Zeiss, c, ocul. 2. It shows the remnant of the vitel- 

 line membrane (/;. i.) separating the columnar but delicate cells of the 

 follicular epithelium (/: e.) from the yolk (,y/-.). In the yolk are seen yolk- 

 spherules in a protoplasmic network. Tiie transverse markings in the yolk 

 spherules have been made oblique by the artist. 



Fig. 24. — Fully formed ovum containing a second nucleus (.r), probably 

 'about to be employed as pabulum ; from the same ovary as fig. 5. The follicular 

 cpitliciium is much tiiicker on the side adjoining the stroma than on tlie 

 upper side of the ovum. Zeiss, f, ocul. 2. Osmic acid. 



