LYMPHATICS IN FROG LARVAE 61 



are now conspicuous. Figure 24 is from a somewhat dis- 

 tended injection of the lymphatics of the left side of the speci- 

 men shown in figure 23, though the pictures would hardly be 

 thought to come from two sides of the same larva. The differ- 

 ences in the result on the two sides are evidently due to an 

 exceptional patency of the larger lymphatics on the left, di- 

 verting the fluid to their full capacity, and demonstrating the 

 main features of the system while losing some delicate rela- 

 tions shown on the right. Thus the jugulo-temporal tract is 

 prominent, as are also important relations of the lymph heart, 

 while the ventral and lateral trunks and their connections 

 appear in bold relief. The injection gives valuable informa- 

 tion, but to adopt such a picture as typical for this stage would 

 be misleading, since important features furnished by other 

 injections giving more details are lacking here. 



The case is another illustration of the value of a large col- 

 lection of injections and need of testing and studying varia- 

 tions in many specimens (and even both sides of each) before 

 deciding what is typical for a given period and at the same 

 time consistent with earlier and later stages. 



In describing this stage (Liu-Li, stage 6) it has been neces- 

 sary to refer to several figures for special features, in order 

 to view the structures from more than one point, and because 

 of the lack of full details of some structures in single injec- 

 tions. For this reason, the injection illustrated in figure 25 

 is especially fortunate in showing with exceptional clearness 

 not only the relations of the lymph heart to its immediate 

 afferent vessels (note the resemblance in pattern to the early 

 heart plexus of fig. 5), but also the proximal ends of both 

 jugular and pericardial lymphatics. 



In passing from the stage just considered to one in which 

 the hind limb buds first become visible, the larva grows larger 

 in all proportions, almost doubling in size from 10 mm. to 

 18 mm. in R. palustris (Pollister's late 23), and at the same 

 time further important changes take place which affect the 

 disposition and appearance of the lymphatic system. The tail 

 is now a conspicuous feature of the larva. It forms a free 



