GROWTH OF BLOOD-VESSELS IN FROG LARVAE i i 



Stockard found in fundulus embryos, in which the circulation 

 of blood was inhibited from the start by the use of alcohol, that 

 the vessels of the yolk sac and many of the vessels of the embryo, 

 including the two aortae, are formed, that some of them become 

 much distended, and that they may persist without circulation 

 for many days. While he gives no detailed or careful study of 

 the exact amount of development of the vascular system, or the 

 amount of retraction of vessels, he states ('15, B, p. 586) with 

 reference to the aorta: 



Tlie aorta in old embryos that never had their blood to circulate and 

 in which the heart is actually a solid stream of tissue, grows and attains 

 a well-developed lumen and a wall .lined with endothelium and sur- 

 rounded by concentric fibers of connective tissue, as is shown in figure 

 4 a in the previous paper, drawn from such a specimen. This vessel is 

 very slow to degenerate, in fact, it shows no sign of degeneration and 

 actually persists as long as the embryo is able to exist without a circu- 

 lation, for 30 days or more." .... The function of the vessel as 

 a blood conductor, therefore, seems in these embryos of Fundulus, to 

 have little if anything to do with its early development and not much 

 effect on its ability to survive These facts are most signifi- 

 cant in a consideration of the influence of function on growth and 

 development, auto-differentiation. Here it is seen that the structure 

 both grows and develops in entire absence of function. 



The descriptions of the extent of vascular development which 

 takes place without a blood circulation, as given by these inves- 

 tigators, w^hile meagre and incomplete, agree in the finding of an 

 extensive vascular system, in which at least some of the main 

 vessels appear to have developed sufficiently to give the impres- 

 sion of being fairly similar to the vessels in normal embryos. 

 Thoma ('93, p. 28) recognized, in chick embryos, that there is 

 not only an extensive development of capillaries in the extra- 

 embryonic area, but part of the aorta is well developed before 

 the heart beat commences. 



He offers t\vo possible explanations of the early development 

 of the aorta. One is that there is an inheritance of an anatomi- 

 cal structure which is in agreement with the structure resulting 

 from the action of mechanical forces. He says (p. 28) : 



Man kann somit nur feststellen, dass die vererbte Form sich in 

 Uebereinstimmung befindet mit jenem allgemeinen von mir aufgestell- 



