Fig. 10. Longitudinal and horizontal section of a Scyllium embryo of stage
H. Zeiss C, ocul. 1. Reduced by 1/3. Picric acid specimen.
It shews (1) the structure of the notochord; (2) the appearance of the
early formed band of muscles (_mp´_) in the splanchnic layer of the
protovertebra.
Fig. 11. Longitudinal and horizontal sections of an embryo belonging to
stage I. Zeiss C, ocul. 1. Chromic acid specimen. It illustrates the same
points as the previous section, but in addition shews the formation of the
rudiments of the vertebral bodies (_Vr_) which are seen to have the same
segmentation as the muscle-plates.
Fig. 12.[1] Longitudinal and horizontal section of an embryo belonging to
the stage intermediate between I and K. Zeiss C, ocul. 1. Osmic acid
specimen illustrating the same points as the previous section.
Footnote 1: The apparent structure in the sheath of the
notochord in this and the succeeding figure is merely the
result of an attempt on the part of the engraver to represent
the dark colour of the sheath in the original figure.
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. 14_a_, 14_b_, 14_c_, 14_d_. Figures taken from preparations of an
embryo of an age intermediate between I and K, and illustrating the
structure of the primitive ova. Figs. 14_a_ and 14_b_ are portions of
transverse sections. Zeiss C, ocul. 3 reduced 1/3. Figs. 14_c_ and 14_d_
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. 15_a_. 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.