An investigation of the lymph system and its relations to 

 the primary blood vessels in frog embryos was begun in 1903 

 when the presence of pulsating anterior lymph hearts was 

 demonstrated for the first time, by the writer, to the Associa- 

 tion of American Anatomists (Knower, '03), in young live 

 larvae long before the appearance of hind limbs then thought 

 to mark the earliest appearance of lymph hearts. 



This was shown in embryos which had previously been de- 

 prived of the systemic heart, the lymph hearts then becoming 

 clearly visible at an early stage, which proved to be the same 

 as that of their normal appearance. Similar conditions are 

 obtainable with chloretone poisoning. The advantages of this 

 method for observation of the early lymph hearts and their 

 pulsations were pointed out in 1907 (Knower, '07). 



In 1908 the first demonstration was followed up by the 

 publication of a description of the definite position and pri- 

 mary relations of the anterior lymph heart to the segmental 

 system of the body and to the pronephros, and the origin of 

 the heart from branches of the early segmental veins was 

 noted. The changes in relations in later stages were also de- 

 scribed. In the same year H. Hover also described the appear- 

 ance of the anterior lymph heart in young anuran embryos. 



These studies were made on sections of uninjected larvae, 

 and furnished, chiefly, data on the primary relations of the 

 lymph hearts and the main lymph trunks associated with them. 

 The general plan of the system as a whole in an older stage 

 had been supplied by H. Hoyer in 1905, in three figures with 

 description of the lymphatics injected in the late 2fi-mm. larva 

 of R. temporaria with hind limb buds. (Two of these figures 

 are reproduced here as text figures D and E, p. 70. One is 

 on plate 10.) So a standard of reference for future studies 

 was then at hand. Hover's valuable pictures have accordingly 

 been extensively referred to in papers on anuran lymphatics, 

 ever since; and indeed have been for long the only figures 



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