424 ELEANOR LINTON CLARK 



chicks, thus demonstrating the presence of valves between the 

 lymph heart and its superficial connections. Injections show a 

 still more abundant set of allantoic lymphatics which form a 

 richly anastomosing net-work around the main allantoic blood 

 vessels and their branches, while large lymph ducts accompany 

 these blood vessels back towaj-d the body. Within the embryo 

 the dense plexus of lymphatics around the aorta is now con- 

 tinuous with the deep anterior lymphatics and connects with the 

 jugular vein by means of the thoracic duct. A similar lymphatic 

 net-work surrounds the external jugular vein. The large supra- 

 scapular sac is still present. ^^ 



The study of the lymph-flow and of the character of the lym- 

 phatics in chicks of later stages and after hatching would be 

 most interesting, especially in comparison with the lymphatic 

 system of ducks, since JoUy^^ j^^g shown that the latter birds 

 retain their pulsating lymph hearts and develop lymph glands in 

 the cervical and lumbar regions, while chicks after hatching 

 have neither lymph glands nor lymph hearts. 



RELATION OF PRESSURE CONDITIONS AT VARIOUS STAGES TO THE 



FLOW OF LY.MPH 



In bringing together the results of these experiments on the 

 early lymph-flow and of the observations of injected lymphatics 

 the following stages appear to summarize the varied changes 

 which occur in the lymph circulation and in the form of the 

 lymphatics during this period of development: 



1) Primary stage (in chicks of 5 to 6 days) in which the super- 

 ficial lymphatic system is an irregular capillary plexus. During 

 this period there is no circulation in the superficial lymphatics. 



'1 This is the stage at which Budge first injected the lymph heart in the chick 

 and observed its pulsations, and his conclusion that its function was chiefly 

 concerned with the lymphatic circulation of the allantois was therefore probably 

 correct. Not having observed the earlier pulsation of the lymph heart he was 

 unaware of the role which it plays in initiating and maintaining the early lymph- 

 flow in many of the superficial lymphatics. (A. Budge, Ueber Lymphherzen bei 

 Huhner Embryonen. Arch. f. Anat. u. Phys. Anat. Abt., 1882.) 



^2 J. Jolly, Recherches sur les ganglions h'mphatiqes dea oiseaux. Arch, d' 

 Anat. Microscopique, T. 11, 1910. 



