OBSERVATIONS OF THE LYMPH-FLOW AND THE 



ASSOCL^TED MORPHOLOGICAL CHANGES IN THE 



EARLY SUPERFICIAL LYMPHATICS OF 



CHICK EMBRYOS! 



ELEANOR LINTON CLARK 



Frovi the Anatomical Laboratory of the University of Missouri 



NINE FIGURES 



INTRODUCTION 



Within recent years our knowledge of the nature of the 

 Ijrtnphatic system has been greatly extended. Researches by 

 Ranvier, MacCallum, and Sabin have revolutionized the former 

 conception of lymphatics as vessels which communicated, by 

 direct openings, with the various cavities and tissue spaces, by 

 establishing the fact that the lymphatic system is everj^where 

 composed of closed tubes lined with endothelium. 



Since the publication of Miss Sabin's first article^ which initi- 

 ated the modern investigation of the early development of the 

 lymphatic system, much research has been concerned with the 

 problem of the origin or primary differentiation of the lymphatic 

 endothelium. This question is still under discussion although 

 recent investigations have pushed back the study of the earliest 

 lymph vessels to stages in which it had previously been supposed 

 that no Ijrmphatics were present. 



That the growth of new capillaries, after the primary differen- 

 tiation of the lymphatic endothelium, is accomplished by a proc- 

 ess of sprouting from the endothelium already formed (a theory 



1 Many of the observations recorded in the present paper were presented 

 before the American Association of Anatomists, at St. Louis, Mo., December, 1914. 

 An abstract was printed in the Proceedings of the meetings, Anat. Rec, voL 9, 

 no. 1, 1915. 



2 F. R. Sabin, On the origin of the lymphatic system from the veins and the 

 development of the lymph hearts and thoracic duct in the pig. Amer. Jour. 

 Anat., vol. 1, 1901-02. 



399 



