."> I ... - ibin. 



There Is a rapid »n of these blood-filled structures, and soon, in 



u an hour ami a half after their lirst appearance, connections between 



bborlng clusters maj a Injection a1 this Btage with India ink 



iws an anastomizing plexus, connected, as before, with the Intersegmental 



reins. Injection with silver nitrate shows distinct endothelial markings 



in the walls of the plexus. 



During this plexus formation there is a steady extension toward the sur- 

 fai '.and by the time anastomoses have formed betv shoring (-lusters 



sprouts havi grown to the surface and Btarted to extend In the region 

 superficial to the plexus and also ventralwards. It now bt possible 



jtudy with more minuteness the changes which are going on. since these 

 sprouts are quite superficial and arc developing in a plane parallel with 

 the surface. Observation and successive records of these sprouts in the 

 living chick reveal a rapid extension ventrally ami also anteriorly, ac- 

 companied by a pit xua formation. Two or three sprouts are seen to lead and 

 soon numerous connections develop hit ween them. Various iwrtions of the 

 Irregular plexus thus formed enlarge and become more densely packed with 

 blood which continues to back up from the vein. Then new sprouts grow 

 out in advance and the same process of extension accompanied by plexus 

 formation is repeated. If a single sprout is selected and frequent careful 

 drawings are made the changes are seen to be rapid and striking. The 



rout becomes wider and longer. Branches appear, and they in turn in- 

 crease in width and length. From a branch a connection forms with the 

 original sprout, thus forming a loop. New branches and connections are 

 formed, making a plexus. Branches from neighboring loops or plexuses 

 meet one another and anastomose. The several parts of the plexus are 

 rpiite irregular in size. Most of the lymphatic vessels are several times as 

 wide as a blood capillary, while some of the connections are as small as, 

 or even smaller, than a blood capillary. Throughout the blood in these new- 

 forming lymphatics is markedly darker in color than the circulating blood. 



This work thus corrects the idea that lymphatics arc transformed 

 blood capillaries. They bud oui from the veins as Lymphatics ami 

 gradually invade the body as a new type of vessels. 



Miller's work (97) mi the anterior lymph sac is chiefly valua 

 in giving an excellenl chance to contrast the method of reconstruction 

 with the method "f injection in an ana where an injection can be 

 obtained. Figure I I is cop m Miller's fig. <;. and li.ir. 1"> i> from 



an injection hy E. I.. Clark's (27, fig. 2 ) of the plexus in the same 



The |"'int- of the apparently isolated islands of lymphatics 

 ami the separation of the sac from the veins show by .Miller are errors 

 which are cleared up by 1-'.. I-. Clark*- work. The jugular lymphatic 

 plexus i- connected with the vein in a number of places and is a con- 

 tinuous endothelial-lined plexus of lymphatics. 



