44 HENRY MCELDERRY KNOWEK 



that in injections, where terminal centrifugal lymph vessels 

 are invariably fine filaments. 



In the reconstruction the ventral lymph chain is represented 

 as still unconnected with the lateral lymphatics, a late union ! 



The aberrant position of the main dorsal lymphatic in the 

 reconstruction, lifted high above the cord, separated from it 

 like the dorsal venous loops in injections, is confusing. 



In addition, the omission of both dorsal veins and lym- 

 phatics from all reconstructions of the anterior region is most 

 unfortunate, in making it impossible to trace the dorsal lym- 

 phatics into the lymph heart plexus, or, on the other hand, 

 important connections of the adjacent first intersegmental 

 veins with other veins. 



Of the four species of frog studied R. palustris, R. pipiens, 

 R. catesbiana and R. clamitans the small 7-mm. larvae of 

 the last two forms most closely resemble the 7-mm. toad. 



The anatomical characters of all three of these larvae are 

 decidedly advanced in development beyond the early primary 

 stages of the frogs examined by injection, as evidenced by 

 the conspicuous intestinal coil, the marked distention of cavi- 

 ties and their surrounding connective tissues, and by the 

 growth of the tail. The lymphatic system in these specimens 

 of 'frog is also advanced in development. 



The specimen illustrated in figure 13 of the present paper, 

 for a 7-mm. larva of R. catesbiana, next to be described as 

 representing the third lymphatic period of the frog (figs. 14 

 and 15 are drawn from somewhat later larva of the same 

 period) exhibits the same characters as the corresponding 

 7-mm. toad larva. 



In the frog, the lymphatics have been traced in injections 

 through earlier stages while gradually becoming adjusted in 

 a system spreading from a single center. 



In the toad, on the other hand, reconstructions suggest a 

 sudden origin of the system in the relatively late 7-mm. larva, 

 and from separate centers, which arise by different methods, 

 and pass through a series of still later modifications (unlike 

 the frog) before forming a complete system. 



