PLATES 16 AM) 17 



EXPLANATION OF FIGURES 



Plates 16 and 17 illustrate the developmental stages of the posterior lymph 

 hearts. In figure 32 the lymphatics are shown before the appearance of posterior 

 lymph hearts as a strongly-injected irregular fine-meshed plexus overlying ;he 

 veins, which are faintly drawn in a wide-open regular plexus. This specimen is 

 from R. palustris of about 10 mm., with globular body. Figure 33 exhibits vhe 

 caudal lymphatics of the 12-mm. R. palustris. The two small posterior hearts en 

 small vessels of the lymph plexus ventral to the main caudal lymphatics art- 

 injected in their first stage. Figure 34 is an injection in the stage like that of 

 figure 30, 18 mm. enlarged to show the details of the lymphatics and the relations 

 of the posterior hearts of this period. The vessels of the plexus are beginning ;o 

 assume a segmental arrangement, and many small processes project from the walls, 

 especially around the hearts. In figure 35 the vessels of the plexus tributary to 

 the lymph hearts are arranged in a strictly segmental pattern along the deeper 

 veins. The posterior hearts are now close to the deeper lateral caudal vein shown 

 faintly in the drawing. Processes from the vessels have multiplied greatly, 

 especially around the hearts, as is illustrated in detail in the enlarged inset to 

 the right. Figure 36 is a photograph illustrating the manner in which ilu' 

 processes from the main lymph vessels of the plexus unite to form an extensive 

 network over the surface of the caudal muscles in late larvae. 



117 



