LYMPHATICS IN FROG LARVAE 31 



As the lateral plexus grows back over the posterior seg- 

 ments, a series of processes run out from its dorsal margins 

 and pass up through the adjacent changing connective tissues 

 (Hover's gel), to join similar outrunners from the dorsal 

 lymphatics over the cord, new connections being added as 

 development proceeds posteriorly; and since the connectives 

 thus formed follow the intersegmental veins for the most part, 

 this dorsolateral series along the side of the body becomes 

 adjusted to the segmental arrangement illustrated in the 

 figures. 3 



The entire series is complete in figure 6, with the three 

 anterior vessels well injected and enlarged, while serving as 

 the chief paths from the dorsal lymphatics to the lymph heart 

 since their first establishment. But this primary arrangement 

 is becoming modified, for the rapid development of the dorsal 

 lymphatics creates new conditions steadily increasing the flow 

 of lymph to the front and accumulating an excess of fluid in 

 these vessels w T hich calls for readjustment in their connections 

 with the heart vessels. The anterior connections being already 

 preoccupied, the excess is accordingly diverted through the 

 most direct connection then available. Hence, in figure 6, the 

 third in the series has evidently become the favored path from 

 the front of the dorsal system to the back of the lymph heart. 

 Here, enlarged as the strongest of the series, it joins an ex- 

 pansion of the heart plexus in the union of these vessels with 

 the 'lateral-body-lymph-tract' (details of this are better seen 

 in figure 5, where the vessels have sharper definition). 



In other injections of the same stage a similar diversion 

 from the original segmental arrangement in front is quite 

 frequent and often extreme, as illustrated in figures 5 and 7, 

 where the anterior connections are wholly uninjected and the 



"This method of growth and distribution of lymphatics from the front along 

 the segmental veins at this period is a reminder of the development of the system 

 described for Urodeles (Grodzinski, '27). But, though the pattern of lymphatics 

 becomes segmental, a more direct path than that offered by the veins is main- 

 tained to the pronephros through the longitudinal ducts of the early lymphatics 

 which collect from the dorsal and lateral connective tissue, as the changes in the 

 tissues from front to back along the veins are followed. 



