The younger of these ovaries was from a Scyllium embryo 10 centimètres long, preserved in osmic acid.
A considerable number of nests were present (Pl. 24, fig. 13), exhibiting, on the whole, similar characters to those just described.
A series of measurements of the nuclei in them were made, leading to the following results:—
0.014 mm.
0.014 mm.
0.016 mm.
0.016 mm.
0.018 mm.
0.018 mm.
Thus, if anything, the nuclei were slightly smaller than in the younger embryo. It is very difficult in the osmic specimens to make out clearly the exact outlines of the various structures, the nuclei in many instances being hardly more deeply stained than in the protoplasm around them. The network in the nuclei is also far less obvious than after treatment with picric acid. The permanent ova were hardly so numerous as in the younger ovary before described. A number of these were measured with the following results:—
| Ovum. | Nucleus. |
|---|---|
| 0.03 mm. | 0.014 mm. |
| 0.034 mm. | 0.018 mm. |
| 0.028 mm. | 0.016 mm. |
| 0.03 mm. | 0.02 mm. |
| 0.04 mm. | 0.02 mm. |
| 0.04 mm. | 0.02 mm. |
| 0.048 mm. | 0.02 mm. |
These figures shew that the nuclei of the permanent ova are smaller than in the younger embryo, and it may therefore be safely concluded that, in spite of the greater size of the embryo from which it is taken, the ovary now being described is in a more embryonic condition than the one last dealt with.
Though the permanent ova appeared to be formed from the nests in the manner already described, it was fairly clear from the sections of this ovary that many of the original primitive ova, after a metamorphosis of the nucleus and without coalescing with other primitive ova to form nests, become converted directly into the permanent ova. Many large masses of primitive ova, or at least of ova with the individual outlines of each ovum distinct, were present. The average size of ova composing these was however small, the body measuring about 0.016 mm., and the nucleus 0.012 mm. Isolated ova with metamorphosed nuclei could also be found measuring 0.022, and their nuclei about 0.014 mm.
The second of the two ovaries, hardened in osmic acid, was somewhat more advanced than the ovary in which the formation of permanent ova was at its height. Fewer permanent ova were in the act of being formed, and many of these present had reached a considerable size, measuring as much as 0.07 mm. Nests of the typical forms were present as before, but the nuclei in them were more granular than at the earlier period, and on the average slightly smaller. A series measured had the following diameters:—
0.010 mm.
0.012 mm.
0.014 mm.
0.016 mm.