Anatomy and Development of Posterior Lymph Hearts of Turtles. 85 



Huntington believes, however, that the jugular lymph sacs are 

 "direct derivatives of the early, redundant, embryonal, venous path- 

 ways of the precardinal and postcardinal regions, adjacent to and involv- 

 ing their point of confluence to form the duct of Cuvier." 1 



(2) The theory of the continuous centrifugal outgrowth of four or 

 more venous buds. By improving the methods of Ranvier, Miss Sabin 

 (1902, 1904, 1908) was able to inject the lymphatics of very young 

 pig embryos. By injecting India ink into the subcutaneous tissue of 

 the neck and inguinal regions of pig embryos of 18 mm. and over, she 

 obtained a beautiful series of pictures showing the peripheral growth of 

 the superficial lymphatics. Her investigations convince her that the 

 lymphatic ducts are budded off from the venous system. She says: 

 "The lymphatic ducts bud off from the veins in four places: two in the 

 neck, at the junction of the jugular and subclavian veins; and two in 

 the posterior part of the body, from the vein which enters the Wolfnan 

 body and which is formed by the union of the femoral and sciatic veins." 

 From these four points of origin the lymphatics grow first along the veins 

 toward the skin to form the superficial lymphatic, and secondly along 

 the aorta and its branches to form the thoracic duct and the deeper 

 lymphatic system. 2 



(3) The theory of the splitting off of the lymphatic from the venous 

 system by a process of fenestration. McClure (1908) describes the forma- 

 tion of the lymph sacs and lymph channels in the cat as follows: The 

 anterior lymph sacs are formed "by the separation of parallel venous 

 channels from the embryonic veins by a process of fenestration, and the 

 subsequent conversion of these channels into definite lymph sacs by a 

 process of growth and fusion." The thoracic ducts are formed by "a 

 series of independent outgrowths which first appear along the common 

 jugular and innominate, and then along the azygos veins exactly in the 

 line subsequently followed by these ducts ; these outgrowths are subse- 

 quently split off from the veins by a process of fenestration, in a series 

 of isolated, more or less spindle-shaped spaces, which later become con- 

 fluent with each other and with a process of the jugular lymph sac of the 

 corresponding side to form a continuous system disconnected with the 

 veins, except through the mediation of the jugular lymph sac." 3 



The explanation for these divergent results seems to be found partly 

 in the methods of investigation and partly in the material investigated. 

 After examining a few series of cat and pig embryos, it seems to the 

 writer that the earlier, critical stages of lymphatic development are too 

 masked or passed through too rapidly to warrant us in basing our con- 

 clusions upon the study of the mammalian type alone. The phylogenetic 

 history of the lymphatic system and its relation to the blood vascular 

 system needs more careful study. Huntington (1910) has well said: 

 "Any theory of lymphatic development must agree in its postulates 

 with the phylogenetic facts, as far as they have been definitely estab- 

 lished." Our knowledge, however, of the lymphatic system of the lower 



1 The Anatomical Record, vol. 2, page 25. 



2 American Journal of Anatomy, vol. 3, p. 183. 



3 Anatomischer Anzeiger, Band 32, S. 533 and 542. 



