Fig. 3d belongs to the neck, fig. 3e to the back, and fig. 3f to the tail.
Fig. 4. Section through the region of the tail at the commencement of stage F. × 60 diameters.
The section shews the character of the tail-swellings and the commencing closure of the medullary groove.
Fig. 5. Transverse section through the anterior part of the head of an embryo belonging to stage F (× 60 diameters). It shews (1) the ventral curvature of the medullary folds next the head. (2) The absence of mesoblast in the anterior part of the head. hy points to the extreme front end of the alimentary canal.
Fig. 6. Section through the head of an embryo at a stage intermediate between F and G. × 86 diameters.
It shews the manner in which the medullary folds of the head unite to form the medullary canal.
Fig. 7. Longitudinal and vertical section through the tail of an embryo belonging to stage G.
It shews the direct communication which exists between the neural and alimentary canals.
The section is not quite parallel to the long axis of the embryo, so that the protovertebræ are cut through in its anterior part, and the neural canal passes out of the section anteriorly.
Fig. 8. Network of nuclei from the yolk of an embryo belonging to stage H.