i: ■'•in. 



■ .1 with blood and thai the blood in them was stagnant, in 

 rapidly circulating venous blood. I 

 in- lymphatics invade the -kin in the chick while they are in the 

 i once an advantag . \'<\ means of fine 

 cannul is E. L I was able :■> inject individual vessels of this blood- 



in the living chick and watch the ink flow to the pul- 

 aph heart and then* - veins. These blood-filled vessels 



usual characteristics <>t' lymphatic capillaries, in that they 

 • r and more irregular than blood capillaries, hut the essential 

 in E. h. Clark'.- work is that by using a form in which the lym- 

 i! in the living embryos she discovered a 

 criterion for recognizing lymphatics, namely, th< tanl blood in 



contrasi t" tin- circulating bl 



With this importanl criterion she lias followed back the origin of 



rior lymph In art-. Since Sala ( L31 ) it has been known that 



in the chick the posterior lymph hearts develop opposite t 



bram irst five < (137,p.269). Sala described 



ginning during the sixth day by a hollowing out of 



the mesem iut by watching the living i nbryo 



during the fifth day 1-'.. \\. an. I I-'.. Ij. Clark hav skin 



al veins i- a comparatively □ □ 

 so that brilliant direct illumination enables them to see in I 



of tiny blood-filled buds close to the main coccygeal \<;ii ami 

 Thi ilood in ightly different color 



from the circulating blood. They proved thai are always in 



connection with the parent vein, for a direct injection of them always 

 into the vein, hut no injection i leripheral blood capil- 



laries ever til they bud nil' from the veins ami are filled 



with blood fri the parent vein. It is of course evi- 



dent that tiii- process cam en in the body wall of the chick with 



■ with which every cell division can he followed in the 

 tadpole's tail ; neverthi agnant blood a proved b} u 



tion I al lv till the developing vessels, so that it i- an adequate 



criterion oj of their development. 



By selecting a chick which shows the-e primary lymphat ami 



Qg it under observation under high power in a warm chamber 



E. R. ami E. I.. Clark i •-"• | i have been able to se hi l-filled 



lymphatic buds join with each other to Eorm a deep circumscribed 

 lymphatii of the pi lymph heart. It is clear 



