LYMPHATICS IN FROG LARVAE 73 



Hover ('05, '08, '34), etc. However, a brief account of the 

 history of the posterior lymph hearts is introduced in the 

 following pages. 



DEVELOPMENT OP THE POSTERIOR LYMPH HEARTS 



The lateral lymphatics grow back over the surface of the 

 muscles in early stages, reaching the fourth or fifth segment 

 on the base of the tail when the rounding-up of the body, from 

 coiling of the intestine, has established a sharp demarcation 

 between body and tail, as represented in figure 23 for R. 

 catesbiana, 7.5 mm., and figure 27 for R. palustris (10 mm.). 



The injection in figure 32 exhibits the fine-meshed network 

 of lymphatics which may be demonstrated far back on the 

 tail in this period of development, and the intimate relations 

 of the superficial lymphatic net to the underlying veins are 

 evident. It is, however, difficult to inject both venous and 

 lymphatic plexuses, with connecting vessels, in the same speci- 

 men, since the fluid tends to run exclusively into one system 

 or layer. Hence it can only be stated here that examination 

 of many specimens indicates that such connections between 

 the two systems are to be found in this period as well as 

 earlier (text fig. A, p. 26) and later. 



Usually, the result for this stage is that shown in figures 

 23 and 26, where the finer net is uninjected, and the caudal 

 lymph plexus is spread out on the broadened surface of the 

 base of the tail, with the lateral line collecting duct, and its 

 series of connections with the dorsal and ventral lymphatics, 

 prominent features. 



The lateral caudal lymph plexus now forms a picture like 

 that described by Hover in his original account of the late 

 larvae (Hoyer, '05) before the development of posterior 

 lymph hearts. Hoyer 's original statement has been over- 

 looked in discussions, but these injections positively confirm 

 his observations (also noted in my report on injections, 1913- 

 1914) that the main body of the plexus is established in early 

 larvae as a delicate network in which the lateral caudal col- 

 lecting duct appears before the posterior lymph hearts. How- 



