4 HENRY MCELDERRY KNOWER 



available for any developmental stage of the system in these 

 forms, though illustrating a late and secondary condition in 

 the frog'. 



Evidently pictures of earlier stages were much needed; 

 both to interpret the arrangements of the lymphatics in frog 

 larvae, and for comparison with results obtained in embryos 

 of other forms for the fundamental relations of the system. 



For this, injections alone seemed to promise objective and 

 positive pictures of value, so I undertook to secure a series 

 of injections pushed back into stages showing the very be- 

 ginnings of the lymphatic system in Anura. This has proved 

 to be an extremely difficult undertaking requiring far more 

 time and effort than expected, especially as variations in the 

 technique were constantly introduced, to test the physiological 

 state of the lymphatics injected. 



A report on progress of the work was presented by me 

 before the American Association of Anatomists and printed 

 in the proceedings of 1913-1914. l It included a statement, 

 with demonstrations, of results from the study of injections 

 of fish embryos and larvae of several Amphibia besides the 

 frog, and contributed to questions still debated today on the 

 early lymphatic plexuses, the origin of the lymph hearts, etc. 



The descriptions and discussions in the present paper, which 

 are based on a critical examination of more extensive material, 

 will be found to confirm the earlier statements. 



In 1901 Dr. F. Sabin published her first paper on the cen- 

 trifugal development of the lymphatic system in pig embryos 

 shown by injection. Since that epochal contribution there has 

 been great activity in the investigation of lymphatics in the 

 vertebrates and a considerable literature has accumulated of 

 which only a bare outline necessary to introduce the reader 

 to the main problems and disputes can be given here. 



1 During the later progress of this work a number of demonstrations were given 

 at various times before the American Association of Anatomists, and, especially, 

 at the Marine Biological Laboratory, Woods Hole, in 1925, and in 1929 at the 

 same laboratory to the International Physiological Congress; also before the 

 Anatomists at Nashville in 1927, and in Charlottesville in 1930. 



