LYMPH-FLOW AND LYMPHATICS, CHICK EMBRYOS 435 



Mierzejewski/^ in his studies of injected chick embryos, has 

 described several of the large lymphatic trunks mentioned in the 

 present article, and he states that they make their appearance 

 a day or two later than the original net-like superficial plexus. 

 He appears to think that these larger vessels are laid down in 

 response to heredity and in this connection mentions particularly 

 the earliest lateral trunk which occupies the position of the 

 lateral lymphatic vessel of Amphibians. However, Mierzejew- 

 ski's figures which show first an irregular superficial mesh-work 

 of capillaries and, in later embryos, larger vessels running through 

 the midst of this plexus, seems rather to corroborate the view 

 presented here. 



In studies of mammalian embryos, Polinski^^ found that defi- 

 nite lymphatic trunks develop in various regions of the embryo 

 and in some instances his pictures show" a capillary plexus pre- 

 ceding the formation of these trunks. In recent investigations 

 of the developing lymphatics in pig embryos. Miss Sabin^^ has 

 shown that the posterior part, at least, of the thoracic duct arises 

 from a plexus of lymphatic capillaries. Stromsten's^" injections 

 of the anterior portion of the thoracic duct in turtle embryos 

 show a plexus surrounding the aorta. It seems probable, there- 

 fore, that many of the factors concerned in the development of 

 the lymphatics of the chick are present in other types of verte- 

 brate embryos. Such a theory of origin for the main lymph 

 ducts would serve to explain the many variations in the position 

 of the thoracic duct which have been found in adult human 

 subjects. 



Within recent years there have been many investigations of 

 the development of the lymph sacs and lymph hearts in various 



" L. Mierzejewski, Beitrag zur Entwicklung des Lymphgefasssystems der 

 Vogel. Extrait du Bull, de I'Acad. des Sciences de Cracovie, 1909. 



^^ W. Polinski, Untersuchungen iiber die Entwicklung der Subkutanen Lymph- 

 gefasse der Sauger, in Sonderheit des Rindes. Extrait du Bull, de I'Acad. des 

 Sciences de Cracovie, 1910. 



^3 F. R. Sabin, On the origin of the abdominal lymphatics in mammals from the 

 vena cava and the renal veins. Anat. Rec, vol. 6, no. 8, 1912. 



2° F. A. Stromsten, On the development of the prevertebral (thoracic) duct in 

 turtles as indicated by a study of injected and uninjected embryos. Anat. Rec, 

 vol. 6, no. 9, 1912. 



