412 ELEANOR LINTON CLARK 



back temporarily. Immediately after each beat, however, they 

 moved on faster than ever toward the lymph heart. Between 

 the spasms of muscular movements, when the blood backed up 

 into the lymph heart, the flow in the lymphatics of the pelvis 

 became much slower and occasionally ceased altogether until 

 the return of the next lymph heart contraction. 



In embryos of this stage, the movement of granules in the 

 lymphatics of the side region was anterior, through the axilla, 

 and into the depth, under the shoulder, as in the stage just 

 preceding. In addition, circulation had been established in the 

 plexus dorsal to the shoulder, where injected granules moved 

 anteriorly and dipped into the deep jugular plexus at the anterior 

 border of the shoulder. 



When an embryo of this stage had been injected, it showed the 

 same channel over the side, a newly differentiated channel in 

 the supra-scapular plexus, and also one over the pelvis (fig. 3). 

 The position of this first posterior channel varies greatly in differ- 

 ent embryos; it may occupy a ventral, dorsal, or median position 

 with reference to the rest of the plexus. 



In slightly older chicks, the lymph heart beats have become 

 stronger, the circulation of lymph in the region just anterior to the 

 hip has practically ceased, while the posterior circulation over 

 the pelvis has become more rapid and continuous. The char- 

 acter of the superficial lymphatics in these embryos, as shown by 

 injection, is practically the same as that just described except 

 that no channels are present in the region just anterior to the 

 hip. Instead, the vessels of this region are irregular and much 

 enlarged. 



During this stage, extensions from the supra-scapular lym- 

 phatic plexus have encircled the region dorsal to the shoulder 

 and anastomosed with branches of the side lymphatics. No 

 circulation is yet present in this newly formed posterior portion 

 of the supra-scapular plexus. 



In this stage of beginning lymph heart pulsations and of pos- 

 terior circulation for the pelvic lymphatics, channels also differ- 

 entiate in the lymph heart plexus. Their position corresponds 

 to the paths which the injected granules follow on their way to 



