FIGURE 11. Dorsal view of an embryo with fourteen pairs of mesoblastic somites. The area pellucida and the developing vascular area are shown, the latter having a mottled appearance. The pushing of the head under the blastoderm is also shown. × 20. (Drawn chiefly by transmitted light.) FIGURES 11_a_-11_k_. A series of transverse sections of an embryo of this stage. × 43. FIGURE 12. Dorsal view of an embryo with about seventeen pairs of mesoblastic somites. Part of the area pellucida is represented. (Both transmitted and reflected light were used in making the drawing.) × 13. FIGURES 12_a_-12_g_. A series of transverse sections of an embryo of this stage. × 43. FIGURE 13. Surface view of an embryo with about twenty pairs of mesoblastic somites. × (about) 15. (Drawn with both reflected and transmitted light.) FIGURES 13_a_-13_f_. A series of transverse sections of an embryo slightly more developed than the one shown in Figure 13. × 20. FIGURE 13_g_. A sagittal section of an embryo of about the age of the one represented in Figure 13. × 20. 14. Head of an embryo with one pair of gill clefts; ventro-lateral view. × 13. 15. Profile view of the head of an embryo with three pairs of gill clefts. × 13. FIGURES 15_a_-15_e_. A series of transverse sections of an embryo of about the age of the one represented in Figure 15. × 20. FIGURE 15_f_. A horizontal section through the anterior region of an embryo of the age of that shown in Figure 15. × 20. 16. Surface view in profile of an embryo with four pairs of gill clefts. × (about) 12. FIGURES 16_a_-16_f_. A series of transverse sections of an embryo of the approximate age of the one represented in Figure 16. × 20. FIGURE 16_g_. A sagittal section of an embryo of the age (possibly slightly younger) of the one represented in Figure 16. × 20. 17. Surface view in profile of an embryo at the time of origin of the limbs. × (about) 5. FIGURES 17_a_-17_g_. A series of transverse sections of an embryo of the age of the one represented in Figure 17. × 7. FIGURE 18. Surface view in profile of the head of an embryo slightly larger than, though of about the same state of development as, the one represented in Figure 17. Reproduced here chiefly to show the gill clefts. × (about) 3. 19. Surface view of an embryo somewhat more developed than the one just described. × (about) 3. FIGURE 20. Surface view of an embryo older than the one represented in Figure 19; with well-developed manus and pes. × (about) 5. FIGURES 20_a_-20_j_. A series of transverse sections of an embryo of the age of the one represented in Figure 20. × 7. FIGURE 21. A photograph of a living embryo in the egg, showing the allantois, yolk mass, etc. The embryo is somewhat more developed than the one shown in Figure 20. × ²⁄₃.