Chapter VI · (continued 2)
Reading edition
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;
(2) the junction of the anterior and posterior roots;
(3) the relations of the segmental ducts to the segmental involutions and the alternation of calibre in the segmental tube;
(4) the germinal epithelium lining the body-cavity.