DEVELOPMENT OF VESSELS WITHOUT HEART 177 



were formed. This work was later confirmed, in a general way, 

 by Stockard ('06), although he states that the vascular develop- 

 ment was far from normal. 



Knower ('07) studied the effects of the early removal of the 

 heart and arrest of the circulation on the development of frog 

 embryos. In this experiment the heart was removed by cut- 

 ting. Some of the embryos lived and continued to develop for 

 as long as fourteen days. Many of the main blood vessels de- 

 veloped, although they were irregularly distended and abnormal. 



Patterson ('09) studied the development of the extra-embryonic 

 vascular system in chicks in which the embryo had been pre- 

 vented from forming by making injuries on the unincubated 

 blastoderm. He states (pp. 87-88), ''although there is not the 

 slightest trace of the embryo proper present, yet the vascular 

 system of the area opaca is well laid down, and even large ves- 

 sels are seen to pass inwards to the center of the pellucid area." 

 This is illustrated in figure 7, p. 89, of his article. 



Stockard ('15) made extensive studies, using chemical methods 

 somewhat similar to J. Loeb's on Fundulus embryos. He found 

 that in embryos in which there had been no heart-beat, the aorta 

 developed into a vessel of considerable size, and he mentions 

 that other vessels had also developed. He pictures only a cross- 

 section of the aorta, however, and his reference to the other 

 vessels is very meager. 



It seems clear, then, from the observations of Thoma, and 

 Sabin, that before the circulation of blood commences, a con- 

 siderable development of the vascular system has taken place. 

 This includes, in the embryo proper, the development of defi- 

 nite aortae, of short stretches of the two vitelline veins, of some 

 of the dorsal segmental arteries, of part of the cardinal veins, 

 and certain neural vessels in the head region, while, in the extra- 

 embryonic area, there is present an indifferent net-work of cap- 

 illaries, to which we might add (Lillie, '08, pp. 87-88) the sinus 

 terminalis. This much obviously develops as the result of he- 

 reditary influences. Soon after the circulation starts, certain 

 other arteries and veins begin to be marked out, and extensive 

 further changes take place within a few days. 



