466... DR THOMAS H. BRYCE ON 
Fig. 3. Corpuscle from heart with fibrillar ring. Yolk stained black with iron hematoxylin. Stage 27, — 
Series 84B. 2. x S00. 
Fig. 4. Corpuscle from vessel on surface yolk in vertical section. Stage 27, Series 84B. 5. x 800. 
Fig. 5. Corpuscle with centrosome and sphere from heart; fibrillz of ring appear as equatorial groups of 
granules. Stage 27, Series 84B. 2. x 800. 
Fig. 6. Large vacuolated ringed corpuscle from heart. Stage 30, Series 93C. 3, x 800. 
Fig. 7. Giant corpuscle in vertical section from heart. Stage 30, Series 93C. 3. x 800. 
Fig. 8. Small ringed yolk-free corpuscle with alveolar protoplasm and round nucleus. Stage 30, Series 
93C,3. Ses00! 
Fig. 9, Same in vertical section. Stage 30, Series 93C. 3. x 800. 
Fig. 10. Corpuscle from heart, with centrosome sphere and lobed nucleus and without ring. Stage 30, 
Series 84B, 2. x 900. 
Fig. 11. Giant apparently multinuclear cell from heart. Stage 30, Series 910. 13. x 500. 
Fig. 12. Small eorpuscle with alveolar protoplasm faintly fibrillar. Stage 30, Series 93C. 9. x 800. 
Figs. 13 and 14. Small corpuscles in vertical section, showing groups of granules at equatorial points. 
Stage 30, Series 93C. 5. x 800. 
Fig. 15. Large cell with lobed nucleus. Stage 30, Series 93C. 5. x 800. 
Fig. 16. Small cell apparently being budded off into vascular space (v.) on surface of yolk cells (hy). 
Stage 30, Series 93C. x 800. 
Fig. 17. Cell with polymorphic nucleus centrosome and sphere in space on surface of yolk cells (hy). 
Stage 30, Series 93C. 4. x 500. 
Fig. 18. Erythroblast with basophile protoplasm, and faint circumferential fibrillation. Nucleus with 
some closely-grouped, larger, and darker-staining karyosomes, and more distinct intervening reticulum. Stage 
32+, Series 113C. 24. x 800. 
Fig. 19. Same in vertical section. Stage 32, Series 113C. 35, x 800. 
The character of the nucleus in both these cells is markedly different from that of the nucleus of the 
similar elements of earlier stages, figs. 13 and 14. 
Puate II, 
Fig. 20. Portion of splanchnic mesenchyme near its developing edge. Stage 31+, Series 106C. 11. 
x 400. Below is mass of yolk cells (hy) with nuclei and yolk grains, and very indistinct cell outlines ; 
above, the mesenchyme consisting of fixed and free cells, and showing spaces filled with blood corpuscles. 
Fig. 21. Section, through the mesonephros and adjoining parts. Stage 31+, Series 106C. 35. x 400. 
To right, the notochord (N.), aorta (A.),-and cardinal vein (C.V.); to left, the inner outline of the 
muscle plate (m.p.). 
Fig. 22. Section of the splanchnic mesenchyme at point M, text figure 2. Stage 32+, Series 1130, 29. 
x 500. Below and to left is mass of yolk cells (hy), above is the line of the mesepithelium (spm.). 
The free cells of the mesenchyme have almost all become polymorphonuclear, and a number are coarsely 
granular. 
Fig. 23. Section through the mesenchyme between aorta and pronephric duct dorsal to cardinal vein 
(cf. text figure 4). Stage 32+, Series 1130.34. x 700. To left, outline of pronephric duct (P.D.); the 
section passes through an opening from the venous sinus round the duct into the cardinal vein (C.V.). 
Puate III. 
Fig. 24. Another portion of nephric tract of mesenchyme. Stage 32+, Series 113C. 34. x 600. 
Below, a typical erythroblast (ery.); above and to the right, a large mononuclear (/m.), contrasting in size 
with the smaller polymorphonuclear cells, ; 
Fig. 25, Section through payt of venous sinus round pronephric duct in region of pronephros. Stage 32+ 
