PLATES 14 AND in 



EXPLANATION OF FIGURES 



Figures 30 and 31 illustrate the lymphatic system of 18-mm. E. palustris in a 

 transitional period preceding the later larva of Hover's well-known figures. At 

 this stage the dorsal lymph system still connects far forward with the anterior 

 lymph heart, and the dorsal plexus has not yet acquired the indefinite character of 

 the later stage. An anterior accessory dorsal system is here well shown in both 

 figures over the brain and sense organs. The lateral body lymphatics are very con- 

 spicuous, shifted to their new position on either side of the dorsal structures, the 

 earlier connections being retained with the median dorsal duct. However, the con- 

 necting vessels now run across the structures of the back, instead of on the surface 

 of the lateral muscles, as before. Body wall lymphatics have formed plexuses 

 around the heart and have invaded the head, in the outer wall of the branchial 

 cavity. This figure also shows the caudal plexus, in which posterior lymph hearts 

 are developed, ventral to the lateral caudal trunk which passes forward to union 

 with the ' lateral body lymphatic. ' The temporal sinus is greatly enlarged and 

 its delicate processes ramify in the tissues below the eye in figure 30. The mternal 

 visceral lymphatics described in the text are drawn somewhat faintly in figure 31. 



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