The sections shew (1) the atrophy of the post-anal section of the alimentary tract (9_b_, 9_c_, 9_d_). (2) The existence of the segmental tubes behind the anus (9_b_, 9_c_, 9_d_). 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 9_c_ but reappears in 9_d_. (3) The downward prolongation of the segmental duct to join the posterior or cloacal extremity of the alimentary tract (9_b_). 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.[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.