DESCRIPTION OF PLATES. 



PLATE 1. 



Fir,. 16. A living chick of 5 days 16 hours. Measurement 16.5 mm. (fresh specimen). X 5. The square indicates the 

 region shown in figure 17. 



FIG. 17. Posterior part of pelvis and tail region of same embryo, showing the two sets of superficial vessels visible in 

 living specimen. Blood-capillaries orange-red in color, lymphatics deep red. The arrow indicates direction 

 of blood-flow in the blood-capillaries. The blood in the lymphatics is stagnant. X 24. 



FIG. 18. Chick of 5 days 12 hours. X 3. The portion posterior to the dotted line is the region illustrated in figure 19. 



FIG. 19. Tail and posterior pelvic, region of the same embryo. The blood-vessels were injected through one of the 

 vitelline veins. The lymphatic plexus remained filled with stagnant blood. The drawing was made 

 from the fresh specimen immediately after injection. The deeper lymphatics of the posterior lymph-heart 

 plexus are shown in paler red, the more superficial capillaries in brighter red. X 18. 



PLATE 2. 



FIG. 20. Chick of 5 days 22 hours. The lymphatic plexus in the posterior lymph-heart region and over the posterior 

 tip of the pelvis, is injected with India ink. X 24. The square indicates the region shown in figure 21. 



FIG. 21. Tail and posterior pelvic region of the same embryo. The lymphatic plexus in the posterior lymph-heart 

 region, and the more superficial plexus connected with it, were injected directly with India ink without 

 disturbing the neighboring blood-vessels. A superficial lymphatic plexus; B and C lymph-heart 

 plexus; D points at which cannula was inserted to make injections. X 36. 



FIG. 22. Posterior half (left side) of a chick 5 days 15 hours old. Measurement before fixation 16 mm.; blood-filled 

 lymphatic plexus present in the tail region and over the pelvis and hip. The embryo was bled and the 

 drawing of the blood-filled lymphatic plexus made from the fresh specimen. X 36. 



PLATE 3. 



FIG. 23. Chick of 5 days 18 hours. X 2.5. The portion posterior to the lines is the region shown in figure 24. 



FIG. 24. Tail and posterior pelvic region of the same embryo. Double injection. Blood-vessels completely injected 

 with India ink (black in the drawing). Lymphatics injected with silver nitrate 0.5 per cent (white in 

 the drawing). The lines A and B indicate the plane of the section shown in figure 25. 



FIG. 25. Thick cross-section through the tail region of the same specimen; i.e. a. intersegmental coccygeal artery; 

 i.c.v. intersegmental coccygeal vein. The superficial blood-vessels are dark in the drawing and the 

 lymphatics white as in figure 24. X 36. 



PLATE 4. 



FIG. 26. Microscopic drawing (oil immersion) of a portion of the lymph-heart region of a chick of 4 days 23 hours, 

 measuring 12 '^ mm. before fixation. The blood-vessels were completely injected with India ink. The 

 specimen was sectioned parallel to the surface and the sections stained with Ehrlich'shematoxylin, counter- 

 stained with eosin, orange G. and aurantia. The figure shows a portion of a lymphatic capillary 

 and of a blood-capillary, containing ink granules, and the adjacent mesenchyme cells, lym. lymphatic; 

 I.n. lymphatic nucleus; b.v.n. blood-vessel nucleus; m.n. mesenchyme cell nucleus. X 1,200. 



FIG. 27. Higher power drawing of the nucleus of a lymphatic endothelial cell (1. n.), and of the nucleus of a mesen- 

 chyme cell (m.n.). X 1800. 



FIG. 28. Microscopic drawing of a chick of 5 days \ hour, showing an early lymph-vessel of the posterior lymph- 

 heart region and its connections with an injected blood-vessel; lym. lymphatic; b.v. blood-vessel; 

 con. connections between lymphatic and blood-vessel; I.n. lymphatic nucleus; r.b.c. red blood-cells 

 inside of the lymphatic vessel. X 800. (Magnification of original drawing 1 to 1200.) 



FIG. 29. Microscopic drawing of a chick of 4 days 23 hours, showing an early lymph-vessel of the lymph-heart plexus 

 with an endothelial nucleus undergoing mitotic division. X 800. (Magnification of original drawing 

 1 to 1200.) 



PLATE 5. 



FIG. 30. Oil immersion reconstruction of the vessels of the lymph-heart region in a chick of 4 days 23 hours; meas- 

 urement 12J mm. before fixation. The early lymphatic plexus is shown in blue. The injected 

 blood-vessels are shown in lines. X, connections between lymphatics and blood-vessels. X 320. 

 (Magnification of original drawing 1 to 800.) 



PLATE 6. 



FIG. 31. Oil immersion reconstruction of the vessels of the lymph-heart region in a chick of 4 days 9 hours; measure- 

 ment 11.75 mm. before fixation. Probable lymphatics in blue. Injected blood-vessels in lines. X, con- 

 nections between lymphatics and blood-vessels. X 320. (Magnification of original drawing 1 to 800.) 



FIG. 32. Oil immersion reconstruction of the earliest lymph-vessels in the region of the posterior lymph-heart of a 

 chick of 4 days 7i hours. Measurement before fixation 9 mm. The probable lymph-vessels are blue. 

 Injected blood-vessels indicated in lines. X 320. (Magnification of original drawing 1 to 800.) 



PLATE 7. 



FIG. 33. Operated chick of 7 days. At 2 days 14 hours incubation five segments anterior to the posterior limb-bud 

 of the right side were dissected away. The next two segments and the anterior half of the limb were 

 left intact, and the next succeeding three segments, opposite the posterior part of the leg, were removed, 

 together with the posterior half of the leg. The tail was then removed. This is an example of the type 

 of embryo obtained from operation 4. X indicates an exposed portion of the spinal cord located at 

 about the midline of the back. X 20. 



