134 ADAM M. MILLER 



Huntington again in 1911 confirmed and elaborated his for- 

 mer view by extensive observations on reptiles (2) and the cat, 

 stating specifically on page 13 of the first number of the Memoirs 

 of The Wistar Institute (3) that "the entire extensive system of 

 lymphatic vessels proper of the adult animal, including the tho- 

 racic and right l}miphatic ducts and their tributaries, is formed by 

 the confluenceof the extravenous intercellular mesodermal spaces," 

 and that "these spaces are lined by a lymphatic vascular endothe- 

 lium which is Jiot derived from the hemal vascular endothelium, 

 but develops independently of the same," and giving his summary 

 and conclusions in remarkably clear terms on pages 153-171 of 

 the same publication. He also points out that the systemic lym- 

 phatic development in the mammalian embryo is "by no means 

 confined to the immediate environment of degenerating embryonic 

 veins. The same field, which shows the above described histo- 

 genetic processes in the development of extra-intimal lymphatic 

 spaces surrounding and replacing a decadent venule, will at the 

 same time contain numerous equivalent lymphatic mesenchymal 

 clefts and spaces which continue to develop independently of 

 any association with retrograding veins" (p. 49). 



Sabin in 1912 (24) still maintains that "the thoracic duct (in 

 the pig) arises in part as a downgrowth from the left jugular 

 sac and in part from a plexus of lymphatics which buds off from 

 the veins of the Wolffian body" (p. 336). 



Recently Kampmeier (15), after studying serial sections of both 

 uninjected pig embryos and one of Sabin's injected specimens, 

 concluded that 



the actual genesis of the thoracic duct is initiated by the appearance of 

 blind mesenchymal Ij^mphatic spaces either around or not immediately 

 in contact with the venous derivatives, or veno-lymphatics, which become 

 detached from their venous trunks and break up into degenerating seg- 

 ments .... During their inception and growth the walls of the dis- 

 continuous thoracic duct anlagen are composed of mesenchymal cells 

 .... Injected specimens of the early lymphatic stages certify the 

 reality of blind uninjectible anlagen beyond the farthest points to which 

 the injecta have penetrated, demonstrating that discontinuities in a 

 developing lymphatic channel are not 'appearances' found only by the 

 study of uninjected embryos (pp. 463-464). 



