468 ON THE ORIGIN AND EARLY DEVELOPMENT 



injected into one of the lymphatics of the anterior side plexus in the living chick 

 moved anteriorly and disappeared in the axillary region, thus showing that lymph- 

 flow had begun. Complete injection of these lymphatics showed that a plexus 

 was present, normal in appearance for a chick of 65 days, with a channel differen- 

 tiated from the primitive plexus in the position of the path taken by the injected 

 ink granules. More posteriorly an extensive plexus, continuous with the side 

 plexus, was injected over the pelvis. At the 

 posterior tip of the pelvis, however, where in 

 a normal chick with a beating lymph-heart a 

 rich plexus is present with one or more definite 

 lymph-ducts differentiated, the operated chicks 

 showed an indifferent, net-like plexus, com- 

 posed of very fine capillaries with delicate, blind YO V alb Fio. 4. Chick of 3 days; 37 



. ' %V \ somites. The stage of 



endings characteristic of the terminal border ao .pSvv V operations i and 2. a.i.b., 

 of a plexus. 



In operated chicks which developed still . 



farther, this most posterior portion of the super- j U\\ : A For p eration a.somites 17 



1 . r . V,V, to 20 were dissected away 



ficial lymphatic plexus, while still primitive in and the wing-bud cut off. 



character, was more extensive, and frequently 



the plexuses from the two sides were found to anastamose over the stump. No 

 connections between the lymphatics and veins of this posterior region were injected 

 in the operated specimens, no channels differentiated from the pelvic plexus, and 

 in no case did a new lymph-heart differentiate. 



In tailless chicks of the early stage of development, in which the early anterior 

 plexus alone could be injected, stagnant blood was frequently found in the vessels 

 of this region. No blood was ever found in the lymphatic plexus which appears over 

 the pelvis in older embryos. By the time a continuous plexus from axilla to stump 

 is present, the circulation has started in the side plexus and has washed the blood out 

 of these lymphatics; while the posterior part of the plexus, having no connections 

 with veins, does not receive any stagnant blood. 



The results obtained from this operation are as follows: 



When a point of origin for lymphatics (in this case the posterior lymph-heart 

 region) is removed at a stage before any lymphatics have developed, the neighboring 

 region (in this case the posterior tip of the pelvis), normally supplied from this 

 point of origin, receives its lymphatic supply by ingrowth from another point of 

 origin (more anterior lymphatics). This conclusion appears to follow from the 

 delayed appearance of lymphatics over the posterior part of the pelvis and from the 

 difference in their character shown by the delicate, blindly-ending tips. Although 

 the region removed is one in which connections between lymphatics and veins are 

 present normally from the earliest stage and maintained throughout embryonic life, 

 the lymphatics which eventually develop over the stump in these tailless chicks do 

 not show any connections with veins in injected specimens. 



An interesting side result came from studying the conditions of lymph-flow 

 in this series of operated chicks in comparison with the conditions present in normal 



