300 GEO. S. HUNTINGTON 



is often delayed until the 24 mm. or 25 mm. period. The deep 

 lymphatics of the anterior limb-bud, developing relatively late, 

 empty into the reduced axillary sac and attain their venous con- 

 nection through the same and the proximal subclavian lym- 

 phatics uniting the axillary and jugular sacs (fig. 17). 



This. brief genetic history of the primitive ulnar lymphatic is, 

 within the normal range of embryonal variation, repeated with 

 remarkable consistency in a very large series of closely graded 

 embryos of the domestic cat. The details, with the evidence 

 presented by the sections and reconstructions, will shortly be 

 published in extenso in one of the Memoirs of The Wistar Insti- 

 tute of Anatomy. • 



For the purpose of the present communication it will suffice 

 to generalize the following conclusions: 



1. In certain regions lymphatic vessels develop during the 

 early embryonal stages, primarily for the purpose of conveying 

 the cellular products of the haemopoetic mesenchymal areas by 

 direct channels into the venous circulation, functionally these 

 early lymphatic vessels are essentially haemophoric. During the 

 period of this functional activity they offer no morphological 

 criteria differentiating them from the adjacent haemal channels. 

 Both the embryonal veins and the related haemophoric lymphatics 

 are engaged in conveying red blood cells to the systemic venous 

 circulation. 



Much of the confusion of terms and of interpretation found 

 in the records of the earlier investigations into the development 

 of the lymphatic system is due to the misconception of this 

 early functional character of these primitive lymphatics. They 

 have, owing to their blood-cell contents, been classed indis- 

 criminately as venous tributaries. In the course of further 

 development these early haemophoric lymphatics may, after 

 performing their primitive function, atrophy completely and dis- 

 appear as components of the definite lymphatic system. This 

 happens in the case of the proximal portion of the primitive 

 ulnar lymphatic of the mammal, as above described. In other 

 instances the early haemophoric lymphatics, after conveying the 

 developing blood cells to their destination within the lumen of 



