LYMPH-FLOW AND LYMPHATICS, CHICK EMBRYOS 437 



lymph hearts in Amphibians are formed from- two or three 

 lymphatics instead of from a luxuriant plexus, as in birds and 

 mammals. However, Knower*" and Kampmeier^^ state that in 

 frog and toad embryos the anterior lymph heart is formed from 

 numerous lymphatic capillaries. The majority of recent 

 investigations, therefore, seem to show that the lymph sacs of 

 mammals and the pulsating lymph hearts of Amphibia and 

 birds are secondary structures whose appearance is preceded 

 by a plexus of lymphatic capillaries. 



The manner in which the lymph sacs are formed from a capil- 

 lary plexus has been named 'confluence' by Ranvier*^ ^nd con- 

 sists in the gradual enlargement of various vessels of a plexus 

 until the walls between them become thin trabeculae and are 

 finally absorbed. The method of formation of those lymph 

 sacs and hearts connected with the veins is similar to that of the 

 subcutaneous lymph sacs of Amphibia, which has been described 

 by Goldfinger.** 



In the present study it has been found that the method of 

 formation of a lymph sac is essentially the same, no matter what 

 its location or relation to the veins. The only difference is found 

 in the case of the posterior lymph sac in the tail, which develops 

 muscular walls and is the only real lymph heart present in the 

 chick. The formation of all the lymph sacs studied in the chick, 

 including the lymph heart, is preceded by a primitive plexus of 

 lymphatic capillaries and by a stage of increasingly rapid cir- 

 culation during which certain of the capillaries enlarge to form 

 channels. The sacs are then formed by the enlargement of a 

 single channel or, more frequently, by the expansion and con- 

 fluence of neighboring channels. In the deep jugular plexus 

 that vessel next the vein, which has served for approximately 

 48 hours as the main duct, gradually enlarges to a sac-like form. 



30 H. McE. Knower, Anat. Rec, vol. 8, no. 2, 1914. 



31 O. F. Kampmeir, On the origin of lymphatics in Bufo. Am. Jour. Anat., 

 vol. 17, no. 2, 1915. 



32 L. Ranvier, Morphologic et developpement des vaisseaux lymphatiques 

 chez les Mammiferes. Arch. d'Anat. Microsc, T. 1, 1897. 



'3 Gizella Goldfinger, Ueber die Entwicklung der Lymphsacke in den hinteren 

 Extremitaten des Frosches. Extrait du Bull, de I'Acad. des Sciences de Cracovie, 

 1907. 



