LYMPH-FLOW AND LYMPHATICS, CHICK EMBRYOS 421 



lymph-flow was posterior for the ventral part of the pelvis, and 

 anterior for the dorsal portion, while in some chicks this con- 

 dition was reversed. But, invariably, at this stage, there is a 

 point over the pelvis in the vicinity of the lymph heart, where the 

 flow is greatly retarded, and where it is modified by the beating 

 of the lymph heart. 



The injected specimens show a large dorsal side channel and 

 two channels over the pelvis, the larger of these occupying the 

 path in which the lymph-flow had been anterior. Dorsal to the 

 shoulder, the supra-scapular sac has become still larger and 

 small windows remain as relics of its former plexiform character. 

 At the point of 'hesitation' over the posterior part of the pelvis, 

 another sac-like enlargement is present. Both of these super- 

 ficial sacs are much larger than the lymph heart or than the deep 

 jugular vessel under the shoulder (the 'jugular sac') connected 

 with the veins. Injections show a still more extensive cir- 

 culation from the allantois at this stage which evidently has 

 monopolized the greater part of the function of the lymph heart. 

 At this stage the circulation in the superficial lymphatics is 

 greatly interfered with: the fluid is prevented from reaching the 

 posterior outlet because of the immensely increased flow from the 

 allantois, while at its anterior outlet its flow is hindered by the 

 m.echanical obstacle presented by the shoulder joint. Also 

 injections of the deep lymphatics of this stage show that the 

 deep jugular sac receives an abundant lymphatic drainage from 

 the deep vessels of the neck, lungs and heart. As a result of all 

 this interference with the flow in the superficial lymphatics, the 

 pressure in these vessels is greatly increased and, meeting very 

 little resistance from the surrounding tissue, they expand into 

 huge sacs or lakes at every point where an obstacle is encoun- 

 tered. Similar enlargements are also found in certain of the 

 deep lymphatics. 



Unfortunately, in chicks of 9 days and older, the lymph-flow 

 cannot be thoroughly tested on account of the thickness of the 

 skin and the appearance of feathers. At this stage, ink in- 

 jected into the lymph heart is not forced back into the super- 

 fical lymphatics after each pulsation as is the case in younger 



