56 HENEY MCELDERRY KNOWER 



the maxillary (and temporal) plexuses, before they acquire 

 an outlet. These isolated distended vessels are shown in his 

 figure 30 ('22). According to the findings for the toad, no 

 outlet is provided for the isolated sinuses until a relatively 

 late stage, and then through a centripetal duct. This drain- 

 age duct from the temporal lymphatics is shown in Kamp- 

 meier's figure 33 ('22, temp. si. max. prim.) for the 7-mm. 

 larva just before its supposed union with the jugular trunk. 

 Injections offer no support to this theory, since continuity 

 of the jugular trunk with peripheral vessels is shown to pro- 

 vide drainage from their first formation. An explanation 

 for the sinuses of the head must therefore be sought else- 

 where and a survey of the injections already discussed with 

 those for later stages seems to identify the most probable 

 cause to be indirect influences from new conditions set up in 

 the tissues by the great contrast in developmental processes 

 in body and tail during their differentiation, while the body 

 becomes a shortened, inert mass, and the tail acquires in- 

 creased activity. 



The sequence of events seems to me to be as follows : 

 Metabolism in the tail is greatly accelerated as this organ 

 differentiates from the body and expands while becoming 

 more active from stage 3 on. These developmental arid func- 

 tional changes are accompanied by an increase of fluid in the 

 tissues, and soon result in a greater flow of lymph forward 

 through the caudal lymphatics, as these enlarge by new 

 growth. At the same time developments in the head are be- 

 ginning to affect the lymphatics there, as witnessed by their 

 more active growth. 



The effects of the increased lymph flow to the front are for 

 some time largely confined to enlargement of the main vessels 

 already established as favored paths, and to the production 

 of new growths. In addition, reinforcement of the muscula- 

 ture in the walls of the anterior lymph hearts undoubtedly 

 gives added power to accelerate the flow of fluid into the pro- 

 nephric sinus. The eliminative functions of this gland doubt- 

 less aid in the maintenance of balance of fluids in the circula- 

 tory system, but in spite of assistance of various kinds to the 



