VASCULOGENESIS IN THE CAT 25 



injection to be continuous, when injection becomes practicable. 

 From this moment (20 somites in the chick is the earliest recorded 

 'perfect' injection of Evans 44 ) there is a sudden and abrupt end 

 to the production of discrete anlages, contrary to what one would 

 expect from the general gradual transitions in natural processes. 

 All of the endothelium is now continuous, development in the 

 sense of genesis has ceased, and growth alone takes place from this 

 time forward. The moment at which injectibility is acquired 

 is then the critical point in the whole history of endothelium. 



But in view of the many separate anlages, admittedly present 

 in the splanchno-pleure and in the embryo and of the transitions, 

 almost universally observed in natural processes, the possibility 

 must be conceded that a belated vesicle or two of endothelium 

 might conceivably escape a sudden annexation to the injectible 

 system. It becomes, therefore, a 'matter of interest to determine 

 its status after injection has been practised and it has failed, 

 hypothetically, to be injected. A moment before, had it been 

 observed in vitro, or had the blastoderm been sectioned, it would 

 have appeared like any of the other discrete anlages in the 'an- 

 lage.' But the test of injection made, it at once ceases to have 

 a future, it has become an artifact, or if pertinaciously insisted 

 upon, a 'Mayer-Lewis anlage.' Because by a hair's breadth, by 

 the veriest fraction of a second, it failed of concrescence prior to 

 the moment of injection, it is absolutely devoid of vascular poten- 

 tialities, and could never, had the injection been omitted, have 

 joined its fellows and participated in the formation of the vascular 

 system. 



But our belated vesicle loses more than its future, it can hardly 

 be said to have a real present existence. When the injection is 

 made, it stands a chance of never being seen by the injector. 

 The injection is' then 'perfect.' If it is seen, it is an 'artifact,' 

 or the injection is not 'complete.' If it is pointed out by another 

 observer, then again the injection is incomplete, or it is a 'Mayer- 

 Lewis anlage' and has lost a previous continuity with the injected 

 vessels. All possibilities have been thoughtfully canvassed by 

 the exponents of injection, and it can be confidently asserted that 



44 1909, Amer. Jour. Anat., vol. 9, p. 281. 



