LYMPH-FLOW AND LYMPHATICS, CHICK EMBRYOS 429 



direct and the channels straight) the circulation in these pelvic 

 lymphatics was very slow and their form greatly resembled the 

 sacs normally present in this region in chicks of 8^ days — the 

 stage at which the superficial circulation is interfered with. 



Moreover, at all stages up to 9 days (before valves have formed 

 between the lymph heart and its superficial connections) the 

 beating of the lymph heart always exerts a momentary and 

 localized influence on the lymph circulation in nearby channels : 

 when granules are moving steadily posteriorly over the pelvis, 

 a beat of the lymph heart temporarily forces them back. That 

 this effect is produced by the forcing out of fluid in both directions 

 (into the superficial connections as well as into the veins) is 

 shown in cases in which the lymph heart contains ink, for at each 

 contraction a few of the granules are forced back temporarily 

 into one of the superficial channels, while the greater part of the 

 ink is seen to enter the veins. After each lymph heart pul- 

 sation, those granules circulating posteriorly in the nearby super- 

 ficial channels, move more rapidly than ever into the lymph 

 heart. In the older embryos in which the fluid over the posterior 

 part of the pelvis is either moving slowly anteriorly or oscillating 

 back and forth in the large superficial sac, a beat of the lymph 

 heart is followed by a posterior circulation into the lymph heart 

 which continues for a few seconds after each beat. 



3) Condition of the blood circulation. The normal, regular 

 circulation of the blood is a necessary factor for the continued 

 lymph-flow at this early stage. If the blood heart stops beating 

 or becomes irregular during an observation of an embryo between 

 6 and 7§ days, the lymph-flow ceases immediately and does not 

 start up again until several minutes after the blood circulation 

 has become normal again. In such embryos no valves are 

 present between lymphatics and veins and, since the irregularity 

 of the blood heart is associated with a back pulsation and in- 

 creased pressure in the veins, the lymphatics fill up rapidly with 

 blood and in this particular, return to their primitive conditioA. 

 This sudden filling up with blood is most noticeable in the pos- 

 terior lymphatics where the change in the blood vascular cir- 

 culation is also associated with a cessation of the lymph heart 

 pulsations. 



