26 HENRY MCELDERRY KNOWER 



The injection illustrated in figure 4 shows the lymph heart 

 plexus opening into the dorsal wall of the heart through ducts 

 from the ventral margin, and this dorsal connection persists 

 without break through the series of injections as the exclusive 

 afferent portal of the heart in the larval lymphatic system. 

 Vessels are found in other injections connecting the lymph 

 heart with lymphatics adjacent to either its anterior or poste- 

 rior wall, but such vessels are generally quite small, are found 

 only in a very few specimens, and are transient, not persisting 

 to later stages. They appear to mark a more extended early 



Figure A is a drawing of the injected early lymph heart and associated plexus 

 in the second period of B. palustris, demonstrating the numerous connections be- 

 tween the superficial lymphatics and the deep veins of the anterior segments. 



contact between the lymph heart and the ventral vessels of 

 the primary plexus which is lost as the afferent openings 

 become restricted to the dorsal wall. The duct to the anterior 

 wall of the heart in figure 4 is one of these transient struc- 

 tures, its exceptional size the result of over-injection of the 

 connected confluence of ducts in front of the heart. The deep 

 efferent communication of the lymph heart with the third 

 intersegmental vein, and anastomosis of this vein with the 

 second are well shown in the figure. Processes from the ante- 

 rior end of the lymph heart plexus have grown forward in 

 an arrangement already like that of the anterior lymphatics 



