54 DEVELOPMENT OF THE SYSTEMIC LYMPHATIC VESSELS 



2 The lymphatic endothelium is an independent modifica- 

 tion of the mesodermai cells lining the first anlages of the lym- 

 phatic spaces, and is not derived from the haemal vascular 

 endothelium. 



3 I am obliged to deny the assumption that the mammalian 

 systemic lymphatic vessels arise by the confluence of numerous 

 elements detached in course of development from the embryonic 

 veins. 



4 I am obliged to put myself emphatically on record against 

 the assumption that the mammalian systemic lymphatic vessels 

 arise by a progressive sprouting from center to periphery from 

 the endothelium of veins, or from that lining the jugular lymph 

 sacs, or equivalent structures in other regions of the body. The 

 mammalian embrvo offers no evidence of such occurrences. 



