VASCULOGENESIS IN THE CAT 19 



that they are identical with the structures observed by Lewis, 

 absolutely certain that they are not the same as the degenerating 

 vessels of Mayer and Fuchs. The degenerating vessels described 

 by Huntington in the cat have a wholly different appearance 

 and to one familiar with the study of sections, the danger of 

 confusing the two seems inconsiderable. With the aid of recon- 

 struction and the comparison of closely graded embryos to ascer- 

 tain the direction of the process, it is difficult to conceive of a 

 possibility of so gross an error. In passing, I would note that the 

 term anlage has hitherto been applied to the developmental 

 process as indicating the earliest appearance of an organ. It is 

 quite improperly used in connection with regressive structures. 



More recently Clark 30 has published painstaking and elaborate 

 studies of growing lymphatics in the tail of the tadpole, contain- 

 ing many interesting details and in major matters confirmatory 

 of the work of his predecessors. We may therefore conclude that 

 the vessels of the tail fin are formed by sprouting and that there 

 is no evidence for the annexation of mesenchyme cells at this stage. 



The debate is again not as to the fact, but solely in regard to 

 the construction that shall be put upon it, and in particular the 

 degree to which such observations may be extended to endothe- 

 lium in general. 



Goette 31 described the first formation of vessels in amphibia 

 from clefts in the mesoderm, which secondarily acquire a wall 

 from adjacent cells and from intravascular wandering cells. 

 Marshall 32 and Morgan 33 have reached similar conclusions, and 

 recently Studnicka 34 has described the formation of the capillary 

 as a channel in the mesostroma, into the wall of which cells mi- 

 grate eventually forming an endothelium: 



I 



Ganz ahnlich verhalt es sich auch mit den Blutkapillaren, welche 

 jedenfalls sehr friih, wenn das Mesostromanetz noch ziemlich locker ist, 

 zum Vorschein kommen. Die Bilder, die ich an meinen Objekten finde, 

 sprechen durchaus nicht dafiir, dass es ausschliesslich nur die Zellen 



30 1909, Anat. Rec., vol. 3, and 1912, Am. Jour. Anat., vol. 13. 



31 1875, Die Entwickelungsgeschichte der Unke. Leipzig. 



32 1890, Stud. Biolog. Lab. Owens College 2: 1893. Vertebrate embryology. 



33 1897, The development of the frog's egg. New York. 



34 1911, Anat. Anz., Bd. 40, p. 33. 



