266 GEO. S. HUNTINGTON 



I have in mind such problems as the genesis, significance, 

 number and distribution of the adult lymphatico-venous connec- 

 tions or 'taps,' including the consideration of the lymphatico- 

 venous hearts and their modified and reduced representatives. 

 Further, the tentative valuation of the physiological factors which 

 in the successive stages have an important bearing on the deter- 

 mination of the 77iorphological type of the developing vascular 

 system as a whole, and of the lymphatic component of the same 

 in particular. Another important question involves the com- 

 parative study of the apparently divergent and dissimilar con- 

 ditions which, under the same general genetic law and following 

 the same ground plan, are observed in embryos of the three 

 amniote classes. This inquiry includes an attempt to correctly 

 define the mutual structural and physiological relations exist- 

 ing genetically between the haemal and lymphatic components 

 of the general vascular system in embryos of the Amniote 

 vertebrates. 



To the supporters of the first of the general theories of lym- 

 phatic development (the 'centrifugal theory') above briefly out- 

 lined (pp. 260-264) the question of the formation, significance, 

 number and distribution of the adult lymphatico-venous con- 

 nections in any given vertebrate becomes a matter of relatively 

 secondary importance as regards the genesis of these connections. 



If the vertebrate lymphatic system develops as the result of 

 a process of continuous centrifugally directed outgrowth, or 

 budding, or sprouting from the preexisting endothelium lining 

 the embryonal veins, and if this process can start from one or 

 two, or four, or a larger number of points along the embryonal 

 venous pathways, then it becomes evident that in the establish- 

 ment of the adult lymphatico-venous connections the develop- 

 ment must have followed one of two lines: One or more of the 

 original points from which a lymphatic system of this type 

 sprouted from the venous system either (a) retained the original 

 connection of the sprout or sprouts with the veins, as the future 

 avenue or avenues of the adult lymphatico-venous connections, 

 or (b) separated temporarily from the parent endothelial venous 

 channel, and then reentered the same secondarily to establish 



