436 ELEANOR LINTON CLARK 



types of embryos. In Miss Sabin's^i first study of the lym- 

 phatics in pig embryos, she fomid, at an early stage, two pairs 

 of sacs connected with veins. At that time she thought that 

 these two paired sacs, the jugular and the iliac, and the thoracic 

 duct connecting them, represented the primary lymphatic system. 

 In 1906 F. T. Lewis^^ found, from the study of serial sections, 

 that the jugular lymph-sacs of rabbit embryos were preceded 

 by a plexus of capillaries containing blood. He believed them to 

 be blood-vessels which had formed a part of the circulating 

 blood-vascular system at one time and had subsequently separ- 

 ated from it. Later, Miss Sabin^^ found this same primary plexus 

 in sections of early pig and human embryos and Huntington 

 and McClure^^ found similar conditions in cat embryos. In 

 studying, in living chicks, the region in the tail later occupied 

 by the pulsating lymph heart in the form of a sac, Dr. Clark^^ 

 and I observed that the plexus which occupies this region, in 

 stages before the formation of the lymph heart, is continuous and 

 composed of blood-filled lymphatic capillaries instead of isolated 

 portions of formerly circulating blood-vessels. Lately, West^^ 

 has confirmed this observation. In her more recent publications. 

 Miss Sabin" has described similar blood-filled plexuses which 

 remain after the blood-vessels have been washed out with Ring- 

 er's solution, and which precede the formation of the mammalian 

 lymph sacs. According to Baranski^^ and Fedorowicz,^^ the 



21 F. R. Sabin, Am. Jour. Anat., vol. 1, 1901-02. 



" F. T. Lewis, The development of the lymphatic system in rabbits. Am. 

 Jour. Anat., vol. 5, 1906. 



-^ F. R. Sabin, The lymphatic system in human embryos, with a consideration 

 of the morphology of the system as a whole. Am. Jour. Anat., vol. 9, 1909. 



2^ G. S. Huntington and C. F. W. McClure, The anatomy and development of 

 the jugular lymph sacs in the domestic cat. Am. Jour. Anat., vol. 10, no. 2, 1910. 



25 E. R. Clark and E. L. Clark, Anat. Rec, vol. 6, no. 6, 1912. 



28 Randolph West, The origin and early development of the posterior lymph 

 heart in the chick. Am. Jour. Anat., vol. 17, no. 4, 1915. 



" F. R. Sabin, The origin and development of the lymphatic system. Johns 

 Hopkins Hosp. Reports, Monographs, New Series, no. 5, 1913. 



28 J. Baranski, Die Entwicklung der hinteren Lymph herzen bei der Unke 

 (Bombinator) . Extrait du Bull, de I'Acad. des Sciences de Cracovie, 1911. 



23 S. Fedorowicz, Untersuchungen liber die Entwicklung der Lymphgefasse bei 

 Anurenlarven. Extrait du Bull, de I'Acad. des Sciences de Cracovie, 1913. 



