LYMPH-FLOW AND LYMPHATICS, CHICK EMBRYOS 409 



when the egg was first opened) still showed the irregular primi- 

 tive form of the lymphatics of younger embryos, but along the 

 side, near the thoraco-epigastric vein and in the exact path which 

 the granules had followed in the living embryo, was a distinct 

 channel which ran through the axilla, dipping in beneath the 

 shoulder and joining the deep plexus connected with the veins. 

 This earliest channel to differentiate was narrow and winding 

 but always distinctly marked out from the surrounding lymph- 

 capillary plexus (fig. 2) . 



Fig. 2 Injected chick of 5 days, 22 hours (16.5 mm.). Stage of beginning 

 lymph flow in the superficial lymphatics, showing first lateral lymphatic which 

 differentiates in the side plexus, and the primitive character of the remainder 

 of the superficial lymphatics. Arrows in this and subsequent figures indicate 

 the path and direction of the circulation in the living embryo. X 5. 



The earliest specimen in which any definite lymph-flow could 

 be found was one in which blood was present throughout the 

 superficial plexus and injected granules failed to circulate at any 

 point except in the region just posterior to the shoulder, where 

 thej^ moved sluggishly but steadily into the depth, through the 

 axilla. When this embryo had been injected and cleared, a 

 definite channel, larger and straighter than the other lym- 



THE .AMERICAN JOURNAL OF ANATOMY, VOL. 18, NO. 3 



