GROWTH or BLOOD-VESSELS IN FROG LARVAE 



53 



part of the main arteriole or venule of the region. It is impos- 

 sible to predict at one stage, which way a capillary will go — 

 whether it will increase in size, remain the same, or atrophy and 

 disappear; it all depends upon the relation which it bears to 

 the other vessels in existence at the time, and to those which are 

 developed later. The endothelium is equipotential, then, and its 

 differentiation into arteries, veins and capillaries is determined 

 by factors outside the endothelial wall or in the lumen. 



Further evidence for this view is found in the following experi- 

 ments on chick embryos. They were performed to test another 

 point, but the results are sufficiently interesting in their bearing 

 on the problem of blood-vessel growth to deserve brief mention. 



The anterior cardinal view of one side, from a point anterior 

 to the otic vesicle to and including a part of the duct of Cuvier, 

 was dissected out from chicks of two and one-half to three days 

 incubation. The method employed is as follows : Berlin Blue is 

 injected into the vein through a very fine glass cannula. As 



MAY 20-2! 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 23, NO. 1 



