LYMPHATICS IN FROG LARVAE 59 



the abdominal cavity to the left, where it is seen in figures 24 

 and 32, extending back to the ventral base of the tail from 

 its junction with the mid-gut just posterior to the pronephros. 

 In ventral view (fig. 24a) the hind-gut is hidden behind (i.e., 

 dorsal to) the bent left end of the crescent-shaped bag of the 

 mid-gut which extends across the abdomen from its union 

 with the stomach, on the right. The stomach lies immediately 

 in front of the mid-gut here, as in all views of this stage 

 (figs. 23, 26, for pictures of the right side). 



Illustrations of the larva at the end of the brief period of 

 transition (only a few hours) from the elongated to the globu- 

 lar body form are selected from the stage (7|- to 8-mm. R. 

 catesbiana; 10-mm. R. palustris) immediately preceding the 

 appearance of the first spiral coiling in the intestine (Liu-Li, 

 stage 6), which starts in the next stage (about 11 mm., R. 

 palustris) as a pronounced loop in the section which joins 

 mid-gut and hind-gut. (See fig. 24a, Int.Flx., for the location 

 of this first intestinal coil.) The intestinal changes are accom- 

 panied by enlargement and alterations in the shape of the 

 abdomen, to accommodate its contents in their new position. 



The enlargement affects both ventral and dorsal walls, but 

 the dorsal wall does not, in this stage, encroach upon the area 

 occupied by the lateral muscles, this surface being left free 

 for observation of blood vessels and lymphatics. In later 

 stages (figs. 30, 31, etc.), a further expansion of the abdomen 

 raises its dorsal wall almost to the level of the dorsal surface, 

 hiding the lateral muscles. 



Lymphatics in larva with globular body form 



The lymphatic system in the larvae just described (figs. 23, 

 24, 26) exhibits a number of modifications in features studied 

 in stage 4 (figs. 14 and 15) which furnish a transition to the 

 pattern found in advanced larvae at the time of the appear- 

 ance of hind limb buds (figs. 29, 30). 



In the anterior, or older part, of the system, the vessels 

 have enlarged and the proximal ducts are more definite tubes 

 as they approach the lymph heart. The early relations may 



