LYMPHATICS IN FROG LARVAE 69 



Relations of the anterior lymph heart to body wall lymphatics 



in late larvae 



However, to understand the special relations of the lymph 

 heart to the afferent vessels which connect with it and form 

 the surrounding plexus in the anterior body wall, injections 

 of a somewhat younger larva (15-mm. R. palustris), illus- 

 trated in figure 28, are required. In this stage, the heart is 

 fully exposed and the two groups of lymphatics of the ante- 

 rior body wall, which later close around it, are still widely 

 separated and relatively undeveloped. The larger of these 

 two groups is formed in front by long processes, now spread 

 out over the pronephros into the anterior body wall from the 

 periphery of the early plexus (fig. 28). The afferent ducts of 

 the plexus in this specimen are seen more clearly in simpler 

 relations than in the older stages, as they are joined by the 

 jugular lymphatic to form the combined anterior collecting 

 duct (figs. 28 and 27a). 



A large duct extending ventrally from the proximal end of 

 the lateral lymphatic, just behind the heart, forms the central 

 channel of the second group of lymphatics of the anterior 

 body wall, and anastomoses of its branches with the plexus in 

 front will complete the envelopment of the lymph heart. 



An intermediate picture is thus furnished, making it pos- 

 sible to trace the history of the anterior afferent lymphatics 

 and their connections from their origin in the primary lymph 

 heart plexus (figs. 3, 4, 5) through successive stages (figs. 

 14, 15, 16, 26, 27, 28) to that described for the late larva 

 (figs. 30, 31), and to compare this with Hover's later stage 

 (26 mm.). (See text figs. D and E, p. 70.) 



In this review it will be recalled that outgrowths from the 

 lymph heart plexus are first distributed to the anterior divi- 

 sion of the dorsal lymphatics to the jugular lymphatics, and 

 to the plexus in the body wall over the pronephros; and since 

 these vessels begin at the periphery of the heart plexus, their 

 connection with the lymph heart itself is indirect, through this 

 reception group which opens into the dorsal wall of the heart. 



