The works of Francis Maitland Balfour, Volume 1 (of 4)

by Francis M. Balfour

It shews the formation of the liver (l), the structure of the anterior fins (b), and the anterior opening of the segmental duct into the body-cavity (sd).

Figs. 9a, 9b, 9c, 9d. Four sections through the anterior region of the same embryo as 9. Osmic acid specimens.

The sections shew (1) the atrophy of the post-anal section of the alimentary tract (9b, 9c, 9d). (2) The existence of the segmental tubes behind the anus (9b, 9c, 9d). With reference to these it deserves to be noted that the segmental tubes behind the anus are quite disconnected, as is proved by the fact that a tube is absent on one side in 9c but reappears in 9d. (3) The downward prolongation of the segmental duct to join the posterior or cloacal extremity of the alimentary tract (9b).

Plate 12.

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.[227] 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.

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.