GENERAL CONSIDERATIONS 71 



endothelium is concerned, when made for the purpose of estab- 

 lishing a connection between any of the other independently 

 formed anlagen of the general vascular system. 



To sum up : The development of the general vascular system 

 haemal and lymphatic vessels is a uniform process, which con- 

 sists in a local origin (genesis) of endothelium from mesenchy- 

 mal cells and a growth of endothelium after it has once been 

 formed. 



In view of what has been said above, it would therefore ap- 

 pear that the lymphatic problem, in its broadest sense, should 

 not be interpreted in terms either of a venous or non-venous 

 origin, but rather in terms of the uniform phases of genesis and 

 growth which may characterize the establishment of vascular 

 channels in general. 



One of the principal conclusions arrived at in the course of 

 this investigation, is a further substantiation of the view that 

 the continuous lumina of the lymphatics, like those of the hae- 

 mal vessels, are formed by a confluence of originally indepen- 

 dent and discontinuous vascular spaces; a circumstance which 

 proves that the method of injection throws no light upon the 

 actual mode of origin of the lymphatic system. 



The functional role played by the independent lymph vesicles 

 of the embryo has already been described by the writer ('15a) 

 in a former paper, to which the reader is referred. 



