276 GEO. S. HUNTINGTON 



walls are lined by a distinct endothelium. The meshes of this 

 plexus have surrounded the earlier blood-islands, the individual 

 cells of the latter now appear free in the lumen of the plexoid 

 channels, and these have established at numerous points (10 to 14 

 in some of the embryos described and figured by McClure and 

 myself) connections with the pre- and postcardinal veins. This 

 stage, represented schematically in figure 7, I have designated 

 as the haemophoric recipient to indicate the fact that independ- 

 ently formed channels have united into a plexus, established 

 connections with the veins and are beginning to collect the blood- 

 cells of the adjacent haemopoetic mesenchyme, for the purpose 

 of conveying them to the venous circulation. This is the first 

 phase in the haemophoric function of the early mammalian 

 lymphatics. In the following period (fig. 8) the spaces and 

 meshes of the dorso-lateral veno-lymphatic plexus have united 

 into a multilocular sac (9) which is engaged in pouring its con- 

 tents of free red blood-cells into the systemic veins. The period 

 corresponds to what McClure and I described in 1910 as the 

 'stage of evacuation,' and which I will here define as the 'haemo- 

 phoric evacuating stage,^ in contrast to the 'haemophoric re- 

 cipient stage' of figure 7. The subsequent periods develop the 

 complete evacuation of the jugular lymph sacs (10) and their 

 temporary separation from the venous channels (fig. 9), the 

 development of the independent peri-venous anlages of the 

 thoracic duct and the systemic lymphatics {12, 14), and the sec- 

 ondary approach of the lymph sac to the main veins at the 

 definite points of the future lymphatico-venous connections (fig. 

 10). 



Lastly (fig. 11) the lymphsac establishes, on the one hand, its 

 definite and now permanent connections (16) with the venous 

 system at either the common jugular or the jugulo-subclavian 

 venous angles, or at both of these points, while on the other it 

 receives the independently developed paravenous systemic lym- 

 phatic trunks, viz., the thoracic duct (17), the jugular, cephalic, 

 deep cervical and broncho-mediastinal trunks (18). The sac now 

 serves as the common portal of entry of the connected lymphatic 

 system into the haemal division of the entire vascular complex. 



