LYMPHATICS IN FROG LARVAE 29 



In both figures 5 and 6 the fluid has run almost exclusively 

 through the lymphatics to expose, unobscured, a widely ex- 

 tended distribution, with the lymph heart plexus readily iden- 

 tified dorsal to the heart at the center of the anterior system. 

 The plexus is expanded and centrifugal outgrowths from its 

 margins have spread out and added to the anterior system 

 already described, dorsal and lateral extensions back of the 

 lymph heart. This is indeed the period of primary distribu- 

 tion for the lymphatic system. 



Figure 5 gives more details in the plexuses than figure 6, 

 the injection having over-distended the main tracts of the 

 latter at the expense of the delicate plexuses seen in the 

 former. 



In the more complete anterior injection illustrated in figure 

 5, the lymph heart plexus forms a conspicuous network inter- 

 posed between peripheral lymphatics which connect with its 

 margins, and indirectly, with afferent openings into the dorsal 

 wall of the heart. In figure 6 the injection demonstrates two 

 compact groups of vessels at the openings (afferent portals) 

 from the deep surface of the plexus into the dorsal wall of 

 the heart. It should be noted again that the organization of 

 the plexus in this stage is definitely, as before, along two main 

 paths marked by the injected fluid through the network; one 

 along the upper margin, receiving afferent tributaries from 

 adjacent dorsal systems; the other a parallel line in the ven- 

 tral border, collecting from the anterior region. The out- 

 growths from the dorsal edges of the heart plexus in this 

 injection, extending far forward along the side of the brain, 

 are long processes over the ear vesicle. They connect freely 

 with the group ventral to the ear, which form a plexus distally 

 in the anterior body wall over the pronephros, and are con- 

 tinued as the jugular lymphatic. Figure 5 furnishes a good 

 demonstration of the distal plexus over the pronephros not 

 injected in all specimens. 



The jugular lymphatic, like the other peripheral extensions 

 from the central plexus, begins in a strong, well-defined proxi- 

 mal duct which tapers rapidly as it passes out through the 



