OVUM IN THE CAPE AND NEW ZEALAND PERIPATUS. 19 
4. The nucleus becomes vacuolate. 
5. The vacuolate tissue of the nucleus passes to its border 
and there forms a thick wall; the centre of the nucleus in 
which the nucleolus lies is clear and does not stain. 
6. The wall of the nucleus loses its vacuolate structure and 
becomes solid and homogeneous. 
7. During these changes in the nucleus the ovum has 
increased in size, the shell has become thick, and small round, 
highly-refractive yolk-granules have arisen in the protoplasm 
of the cell. 
8. The nucleus acquires an irregular outline, which is caused 
by peripheral portions of its substance passing out into the 
cell plasma, where they are visible as spheres of various sizes. 
9. The whole of the nucleus with the exception of the 
nucleolus breaks up in this way ; the spheres to which it gives 
rise probably become metamorphosed into yolk. 
10. The protoplasm becomes vacuolate, the boundary between 
the egg and its follicular stalk disappears, and nuclei pass from 
the latter into the substance of the former. The nucleolus is 
not visible. 
11. The follicular stalk becomes hollow, and nuclei from its 
walls, and yolk pass along it into the ovum from the ovary. 
12. The follicular nuclei are no longer visible and probably 
become transformed into yolk. 
13. A large nucleus appears in the ovum, lying near its 
point of attachment to the stalk, the boundary between the 
two being again established. The origin of this nucleus is not 
known. 
14, The youngest ovum in the uterus has no nucleus visible. 
15. The origin of the segmentation nucleus is unknown. 
16. No polar bodies have been observed. 
GENERAL CONSIDERATIONS. 
Recently much work has been done on the subject of the 
origin of the ova and the phenomena of maturation and ferti- 
lization. I shall not attempt here to give a complete review 
