• rn i /.'. Sabin. 



lood islands and th< of the meaning of this 



Hid in two works of Bis, " Untersuchung 



ueber die erete Anlage des Wirbeltierleibes " in L868 I »p. 95-103) 



and in " Lecithoblast and Angioblast" in L900 (pp. 868-295). The 



. of blood islands, however, dates back to the work of 



Wolff (154) and Pandei (101), who introduced the name, and 



perhaps do on< : in i mbryologj has a more extensive litera- 



tun I tainly a most iniciv>iinu r iu-cnint of the development of 



vascular problem can be followed through the of von 



I' • rost and Leber! | 108), Remak | L24-125), Reichert 



(121-123), Koelliker (67-71) and Thoma (148). The second 



it advance was the dis lil 1 \i ssels I iui are 



lined b) endothelium (Hoyer 18), which followed soon after the 

 corresponding discovery in lymphatics by von Recklinghausen, 'i 

 third • involves the proof t! ow bj 



sprouting of their em a, I'm . ■ ■ - i and I. (108), Eis 



(47), Rouget (126) and Arnold (5); the fourth that the main 

 vessels of the body wall, including the posterior pari of the aorta 

 (Evans 33-35), even the anterior part of the aorta and lateral hear! 

 anlagen, arise as a capillary plexus or as solid angioblast cords 

 (Bremer 15), which invade the body from the extraembryonal mem- 

 branes. Finally a complete conception of the developmenl of I 

 vascular system is based on thi that the blood vessels of the 



extraembryonal membranes invade the body wall (His II). and 

 that within the body wall th< lillaries of endothelium gradu- 



ally invade or spread over I bod o I al there are definite vascu- 

 lai and niin-\a.Miihir layers and zones. His i 17) discovered the fad 

 that bloi i Is grow into the central nervous ; but the theory 



of vascular and non-vasculai which is essential to an v md- 



ing of the develop al of the vascular system we owe to Mall (80-81 I. 



li iia- been worked out by his pupils, notably Evans (33-i 5). Its 

 meaning can be grasped by studying figs. 4, 5 and 6 in connection 

 with fig. 437 (Evans 35), which all show I skin dorsal to the 



centra] nervous s] • a non-vascular zone, which for a long 



time is nol reached by the blood vessels in the centrifugal growth, 

 of discoveries, notwithstanding the gaps and uncer- 

 tainties in our knowledge of the early stages which were well 

 brought out by Minol (98, pp. 183-485) and by Evans (35, pp. 551- 



.i in 1911, uncertainties in part since removed l>\ the work of 



