64 HENRY MCELDERRY KNOWER 



caudal plexus') lying along the lateral line of the tail in a 

 network of fine vessels to join the coarser plexus in the body, 

 which is now coalescing with the distal end of the body trunk 

 at the base of the tail (fig. 29) in stages preceding that illus- 

 trated in figure 30. 



The 'lateral caudal plexus' has at first an irregular fine mesh 

 with a lateral line trunk running lengthwise. The plexuses 

 in figures 29 and 30, however, exhibit a more advanced organi- 

 zation in relation to a series of posterior lymph hearts which 

 have appeared in them, and the changes which lead to these 

 structures will be discussed in a later section of the present 

 paper. 



Dorsal lymphatics in late larvae 



If the conditions illustrated in figures 30 and 31 for the 

 dorsal lymphatics are now examined with an understanding 

 of the secondary changes in relations outlined above, these 

 vessels are found to have retained their original position and 

 relations while adding new features at the periphery. As 

 previously, the main dorsal duct lies on the surface of the 

 spinal cord, which is now deep between the lateral muscles. 

 The dorsal caudal lymphatic receives many afferents in addi- 

 tion to those from the fin, which have become a complex sys- 

 tem of anastomosing branches. New tributaries enter from 

 the tissues around the cord and from the adjacent muscles, 

 as well as larger vessels from the lateral lymphatic plexus on 

 the surface of the greatly augmented caudal muscles. Pass- 

 ing forward, the median dorsal lymphatic of the body also 

 receives here many new branches from around the cord and 

 the neighboring muscles, and ends anteriorly as in primary 

 stages, in a median dorsal plexus over the posterior surface 

 of the hind-brain at the level of the anterior lymph hearts. 



Anterior accessory dorsal lymph system (Ant.Ac.DsLL.) 



In front of the original plexus of the dorsal lymphatics, an 

 accessory anterior system has spread over the hind-brain, 

 developed from anterior branches of the lymph heart plexus, 



