ORIGIN OF THE POSTERIOR LYMPH HEART 435 



to flow throuj2;h a fistula. He concludes that "the fact that con- 

 necti\-e tissue cells are changed in form bj^ physical agents 

 into flat closely disposed cells, the outline of which ma^^ be de- 

 fined by silver salts makes tenable the conclusion that the ex- 

 posed connective tissue cells * * '^ ' may become flattened 

 by pressure or friction or both." Therefore, mesothelimn and 

 endothelium, both being tissues of mesenchymal origin, owe 

 their production to identical mechanical factors. 



To summaiize: The evidence found from the study of in- 

 jected embryos indicates that the lymphatic plexus which later 

 enters into the formation of the posterior lymph heart, arises 

 by the confluence of independent mesenchymal spaces which 

 connect secondarily with the veins; that these spaces are bounded 

 at first by mesenchymal cells which later become flattened to 

 form an endothelium and that both in the endothelial lymphatic 

 walls and the adjacent mesenchj'-me an active haemopoesis, 

 the products of which reach the general circulation via the lym- 

 phatic plexus, is taking place. 



In conclusion, I wish to thank Professor McC lure and Pro- 

 fessor Huntington wdio have directed this w^ork for their constant 

 guidance and criticism; Professor Schulte and Professor Miller 

 for many valuable suggestions; Dr. McWhorter for the care 

 that he has ex])ended on the microphotographs, and Mr. Peter- 

 sen for his drawings of the very complex reconstructions. 



BIBLIOGRAPHY 



In the order in wliich the articles are mentioned in this paper. 



(Ij Sala, L. 1900 Richerche fatta nel Lab. di Anat., Norm della R. Univ. di 

 Roma, vol. 7, p. 263. 



(2j ^NIiERzEiEVPSKi, L. 1909 Beitrag zur Entwicklung des Lymphgefiiss- 

 systems der Vogel. Bulletin de I'Academie des Sciences de Cracovie, 

 Juillet. 



(3) Stromsten, F. a. (1) 1910 A contribution to the anatomy and develop- 

 ment of the posterior lymph hearts in turtles. Publication No. 132 

 of the Carnegie Institution of Washington, pp. 77-87. (2) 1911 On 

 the relation between the mesenchyme spaces and the development 

 of the posterior lymph hearts of turtles. Anat. Rec. vol. 5, no. 4, 

 April. 



