RELATION OF LYMPHATIC TO BLOOD-VASCULAR SYSTEM 43 



forms, while rudiments of the same are found, as shown by 

 Schulte's and Tilney's observations, in connection with the venous 

 return along the caudal vein only in the Macropodidae. 29 



Schulte's work on the venous organization of the Monotre- 

 mes 32 proves, I think, conclusively the phylogenetic value of the 

 periaortic venous reticulum with axial pathways of hydrostatic 

 selection which the detailed study of placental embryos establish. 

 His dissections of both Platypus and Echidna revealed for the 

 first time the persistence in the Monotreme of both dorsal supra- 

 cardinal channels, and of ventral preaortic vessels of subcardinal 

 and cardinal collateral derivation, while, as appears uniformly 

 throughout the mammalian class, the primitive postcardinals 

 retain normally solely the function of venous drainage for the 

 gonad. 



The facts just stated have been in a large part already pub- 

 lished in outline by McClure, Schulte, Tilney, Darrach and 

 myself. I hope it will be possible to collect the numerous obser- 

 vations, with adequate illustrations, in a publication to be issued 

 in the near future. I have recorded some of the results obtained 

 through these joint investigations in this paper in order to use 

 them for the purpose of clearly outlining on a broad basis the 

 genetic possibilities in the development of the venous system, 

 and the correlated interdependence of the systemic lymphatic 

 vessels. The latter will, in the mammal, take over and further 

 develop territory formerly occupied by transient embryonic 

 venous channels, which they secondarily replace through extra- 

 intimal development. Hence the resulting mirror picture which 

 the lymphatic system of the adult mammal presents in reference 

 to the axial venous trunks, whatever type of central venous organ- 

 ization may obtain in any individual instance. 



The examples just given could, df course, be indefinitely multi- 

 plied. They all show absolutely congruent, uniform and constant 

 pictures in all parts of the body of the developing lymphatic chan- 

 nels in close association with the adjacent veins, but not connected 



32 H. v. W. Schulte: "The Range of Variations in Monotremes and Australian 

 Marsupials." Anat. Rec., no. 3, April 1, 1907. Am. Jour. Anat., vol. vi, no. 

 3, 1907. 



