Fig. 13. Longitudinal and horizontal section of an embryo belonging to stage K. Zeiss C, ocul. 1, and illustrating same points as previous section.
Figs. 14a, 14b, 14c, 14d. Figures taken from preparations of an embryo of an age intermediate between I and K, and illustrating the structure of the primitive ova. Figs. 14a and 14b are portions of transverse sections. Zeiss C, ocul. 3 reduced 1/3. Figs. 14c and 14d are individual ova, shewing the lobate form of nucleus. Zeiss F, ocul. 2.
Fig. 15. Osmic acid preparation of primitive ova belonging to stage K. Zeiss immersion No. 2, ocul. 1. The protoplasm of the ova is seen to be nearly filled with bodies resembling yolk-spherules: and one ovum is apparently undergoing division.
Fig. 15a. Picric acid preparation shewing a primitive ovum partially filled with bodies resembling yolk-spherules.
Fig. 16. Horizontal and longitudinal section of Scyllium embryo belonging to stage K. Zeiss A, ocul. 1. Picric acid preparation. The connective-tissue cells are omitted.
The section shews that there is one segmental tube to each vertebral segment.
Fig. 17. Portion of a Scyllium embryo belonging to stage K, viewed as a transparent object.
It shews the segmental duct and the segmental involutions—two of which are seen to belong to segments behind the end of the alimentary tract.
Fig. 18. Vertical longitudinal section of a Scyllium embryo belonging to stage K. Zeiss A, ocul. 1. Hardened in a mixture of osmic and chromic acid. It shews
(1) the commissures connecting together the posterior roots of the spinal nerves;