VASCULOGENESIS IN THE CAT 23 



between the separate anlages of the vessels in the yolk-sac and in 

 the embryo. 



Very recently Miller and McWhorter 42 have demonstrated the 

 formation of the embryonic vessels in situ and their absolute gene- 

 tic independence of those of the area vasculosa in the chick, by 

 effecting a separation on one side between the body of the embryo 

 and its membranes at a very early period, before vessels have 

 appeared in the area pellucida. In their experiments, the blasto- 

 derm is incised longitudinally near the primitive streak. The 

 wound gapes widely and the area vasculosa is separated from 

 the embryonic body by a wide interval, which no sprouts cross. 

 Notwithstanding which, the embryonic vessels are formed typi- 

 cally, and differ from those of the normal side only in size and 

 rate of development, both of which details may be correlated to 

 their reduced drainage area and the in consequence diminished 

 quantity of circulatory fluid. 



It would seem therefore that the limitations of injection and 

 the data of intra vitam methods are hardly favorable enough to 

 the doctrine of specificity, hardly discordant enough with the 

 findings by the method of slides and reconstruction, 43 to attribute 

 differences of opinion in these matters wholly to the methods 



42 Abstract, Proc. Am. Ass. Anat., Anat. Rec., vol. 8, no. 2. 



43 E. R. Clark has endeavored (Anat. Rec., vol. 3, 1909) to show that fixation 

 gives interruptions in the course of vessels which have previously been ascertained 

 to be continuous by direct observation intra vitam. "A drawing was made of 

 lymphatic and blood vessels during life. The tail was then cut into serial sec- 

 tions ten micra thick, stained in hemotoxylin and Congo-red. In attempting to 

 reconstruct it was found while blood capillaries, could often be fairly well con- 

 structed, it was impossible to reconstruct the lymphatics beyond the muscular 

 margin." In a second paper (Anat. Rec., vol. 5, 1911) Clark shows evidence of 

 retrograde progression in this line of technique, for the blood vessels in his 3, 6, 

 and 7 figures can hardly be considered "fairly well reconstructed." There are no 

 technical procedures that will not miscarry and such tests as Dr. Clark's are 

 critical of personal accomplishment and judgment not of method in the abstract. 

 In view of the technical difficulties offered by amphibian material, and the fact 

 that none of the data on which the theory of concrescense is based are derived 

 from this form, Dr. Clark's criticism is both unfair and far from the point. With 

 the same plausibility he might have proved that good sections could never be 

 cut, because the yolk of frog's eggs is very likely to tear in paraffin. There is a 

 relation between method and material, to disregard which for controversial pur- 

 poses shows more of zeal than of sound reason. 



