Fig. 7_a_ and _b_. Two transverse sections of an embryo about the age or rather younger than that represented in fig. 5. (Magnified 96 diam.) _a._ Section nearer the tail; it shews the thickening of the hypoblast to form the notochord (_ch´_). In _b_ the thickening has become completely separated from the hypoblast as the notochord. In _a_ the epiblast and hypoblast are continuous at the edge of the section, owing to the section passing through the embryonic rim. Fig. 8. Surface view of a spatula-shaped embryo. The figure shews (1) the flattened head (_h_) where the medullary groove is deficient, (2) the caudal lobes, with a groove between them; it also shews that at this point, the medullary groove has become roofed over and converted into a canal. Fig. 8_a_. Transverse section of fig. 8, passing through the line _a_. (Magnified 90 diam.) The section shews (1) the absence of the medullary groove in the head and the medullary folds turning down at this time instead of upwards; (2) the presence of the pleuro-peritoneal cavity in the head (_pp_); (3) the completely closed alimentary canal (_al_). Fig. 8_b_. Transverse section of fig. 8, through the line _b_. (Magnified 90 diam.) It shews (1) the neural canal completely formed; (2) the vertebral plates of mesoblast not yet split up into somatopleure and splanchnopleure. Fig. 9. Side view of an embryo of the Torpedo, seen as a transparent object a little older than the embryo represented in fig. 8. (Magnified 20 diam.) The internal anatomy has hardly altered, with the exception of the medullary folds having closed over above the head and the whole embryo having become more folded off from the germ. The two caudal lobes, and the very marked groove between them, are seen at _ts_. The front end of the notochord became indistinct, and I could not see its exact termination. The epithelium of the alimentary canal (_al_) is seen closely underlying the notochord and becoming continuous with the epiblast at the hind end of the notochord. The first visceral cleft (1_vc_) and eye (_op_) are just commencing to be formed, and the cranial flexure has just appeared. Fig. 10. Section through the dorsal region of an embryo somewhat older than the one represented in fig. 9. (Magnified 96 diam.) It shews (1) the formation by a pinching off from the top of the alimentary canal of a peculiar body which underlies the notochord (_x_); (2) the primitive extension of the pleuro-peritoneal cavity up to the top of the vertebral plates. PLATE 4. Fig. 11_a_, _b_, and _c_. Three sections closely following each other from an embryo in which three visceral clefts are present; _a_ is the most anterior of the three. (Magnified 96 diam.) In all of these the muscle-plates are shewn at _mp_. They have become separated from the lateral plates in _b_ and _c_, but are still continuous with them in _a_. The early formed mass of muscles is also shewn in all the figures (_mp´_).