42 HENRY MCELDERRY KNOWER 



The possibility of frog larvae exhibiting the disjunctions 

 and transformations of systems described for the toad in 

 these active functional stages is readily examined by refer- 

 ence to our series of injections. The results indicate that 

 such a conception of the development of these structures is 

 entirely inconsistent with their differentiation as part of the 

 physiologically organized system shown in injections; also 

 quite atypical for the origin of a major system in lower 

 vertebrates. 



In frogs, the anterior lymph hearts exhibit no breaks in 

 continuity with their main afferent vessels throughout the 

 entire series of injections from their first appearance but, on 

 the contrary, appear to become constantly more intimately 

 adjusted to their function of evacuating the lymph plexus. 

 The entire series of intersegmental veins is present from the 

 first injection, and persists through successive stages, main- 

 tained by a steadily increasing amount of blood flowing out 

 from the neural plexus. 



The absence of the neural plexus and its connections from 

 the reconstructions of the toad, and the incomplete or scant 

 representation of dorsal vessels there, is unfortunate. It re- 

 sults in the neglect of important influences which preserve 

 both the functional and anatomical relations of these veins. 

 The fact that these veins of the anterior segments are demon- 

 strated in the same pictures with the lymphatics in injections 

 discredits the theory of their change of function with trans- 

 formation into lymphatics in the late stage designated. 



In the frog, the stage of early differentiation is illustrated 

 in figure 1, with the anterior lymph heart and its primary 

 plexus still part of the segmental venous system. 



Both lymphatics and veins are again shown in figure 2, the 

 lymphatics exhibiting considerable progress in their independ- 

 ent growth and distribution, while the anterior veins are seen 

 to have acquired new connections which establish them more 

 firmly with no indication of detachment from their primary 

 connections. 



