36 HENRY MCELDERRY KNOWER 



in strongly developed paths like those fixed later. There is 

 also a pronounced diversion of fluid from the dorsal track 

 through posterior connectives, forming much enlarged lateral 

 vessels here, similar to those characteristic of late stages 

 (15 mm. to 18 mm.). 



The fundamental plan for the dorsal system is thus shown 

 in injections of the early period illustrated in figures 3 to 10 

 (and in figures 13 to 26 for older stages) to be characterized 

 by the persistence of the primary anterior connections be- 

 tween the dorsal lymphatics and the lateral heart plexuses 

 until a late stage. The main pathway, whether as a plexus or 

 a single vessel, is being continued far forward to reach the 

 lymph heart plexus (see the 18-mm. R. pal., fig. 31). 



The establishment of fixed paths at the base of the tail, to 

 divert the current from the tail into lateral vessels, is a sec- 

 ondary condition common in late stages (Hoyer, 26 mm., '05; 

 see text figs. D and E, p. 70, which are reproductions of 

 Hoyer 's figures). 



SUMMARY OP DATA FROM INJECTIONS OP THE ORIGIN 



AND EARLY HISTORY OF THE DORSAL AND 



LATERAL LYMPHATICS 



1. Like other plexuses, the dorsal lymphatics reach their 

 region of distribution over the high cervical cord by out- 

 growth from the anterior lymph heart plexus in an early 

 stage, closely following the establishment of the circulation 

 of the blood in the primary system. 



2. A simple lymphatic plexus is first formed. 



3. In this plexus, a prominent median vessel is differen- 

 tiated at an early period, along the mid-dorsal line over the 

 cord, connecting with the lateral lymphatics through many 

 processes. 



4. This median vessel is a path resulting from organization 

 of the plexus through the interplay of histodynamic forces in 

 a functional system in balance with the other lymph plexuses 

 and blood vessels throughout the body. 



