EARLIEST BLOOD-VESSELS IN MAN 461 



nephros (indirectly also those of the mesonephros) , the sex cords, 

 and the cortex of the suprarenal gland, according to the later 

 views. '^ 



The origin of the chorionic vessels from the mesothelium of the 

 body-stalk explains the fact, mentioned by Knoop^^ in anomalies 

 of the amnion, and by Bauereisen'^ in haematomoles, that vessels 

 can exist in the chorion "without the help of the umbilical vessels." 



Let us now turn to a discussion of the papers before referred to, 

 in which the authors describe the results of experiments, on chick 

 or other bird embryos, undertaken to prove the origin in situ of 

 intra-embryonic blood-vessels, as opposed to the extension or 

 growth of such vessels from some extra-embryonic source, by 

 destroying or cutting off the whole or part of the area opaca of one 

 side. Vessels on the injured side are obtained in many cases by 

 all these investigators, after a further incubation of the operated 

 embryos; and these vessels are generally in the position of aorta, 

 heart, vitelline vein, and even other vessels of normal embryos. 

 Wliere only part of the vascular system exists on the injured side, 

 it appears to be always that nearest the mid-line; i.e., the aorta 

 may be present without the heart, or the aorta and heart without 

 the other vessels. Not infrequently the vessels are abnormally 

 large, or the lateral vessels may be only roughly in the normal 

 position. Graper^^ and Hahn,-" though the results of each were 

 known to the other before publication, come to different conclusions 

 as to the origin of the vessels; the first maintaining from his experi- 

 ments, an entodermal, the other from his experiments a meso- 

 dermal derivation. Miller-' is chiefly interested in the negative 

 proof that the intraembryonic vessels do not reach their ultimate 

 destination by direct ingrowths of endothelium from the lateral 

 area, as was maintained in my former paper. 



'« Goormashtigh, N. Bull. Soc. Med. de Gand. Vol. 5, p. 24, 1914. 

 '"Knoop, H. Beitr. Geburtsh. Gynak. Bd. 7, p. 284, 1903. 

 1* Bauereisen, quoted from Jagerroos„ B. H. Archiv f. mikr. Anat. Bd.S2, 

 Abt. 1, p. 271, 1913. 



18 Graper, L. Arch. f. Entw. Mech. Bd. 24, p. 375, 1907. 

 20 Hahn, H. Arch. f. Entw. Mech. Bd. 27, p. 337, 1909. 

 «i Miller, A.M. Anat. Record. Vol. 8, p. 91, 1914. 



