ORIGIN OF BLOOD-VESSELS IN BLASTODERM OF CHICK. 235 



Leboucq (1876), and Wissozky (1877). Ranvier studied the formation of blood- 

 vessels in the omentum of the guinea-pig and in the blastoderm of the chick, and 

 described the vessels as coming from vasoformative cells. He states: 



"C'est generalement dans les points nodaux que se produisent les premieres cavitt's 

 vasculaires et les ilots sanguins. Les premieres cavites vasculaires sont d'abord des creux 

 remplis de liquide qui s'agrandissent et s'allongent pour canaliser les branches du reseau. 

 Les noyaux et le protoplasma refoules a la peripherie constituent les premiers elements de 

 la paroi du vaisseau. Ces elements, agissant a la maniere des cellules glandulaires, secre- 

 tent un liquide, premier plasma du sang, qui distend peu a peu les branches du reseau pour 

 leur donner le diametre considerable dont. nous avons deja park'. Les ilots sanguins se 

 forment aux depens de certaines cellules des cordons vasculaires primitifs qui sont mises en 

 liberte dans leur interieur au moment de leur canalisation. Ces cellules, relativement peu 

 nombreuses, sont spheriques et contiennent d'abord un seul noyau (page 640)." 



With this description I agree, except in considering that the process by which 

 plasma is formed is one of liquefaction of protoplasm rather than a process analo- 

 gous to secretion. Schaefer studied the formation of capillaries in the skin of a 

 newborn rat and described certain vasoformative cells with vacuoles within the 

 cytoplasm in which developed new, disc-like, adult red corpuscles. The latter 

 point is, of course, entirely out of harmony with our present ideas concerning the 

 origin of red cells; it is more in harmony with our ideas of the destruction of red 

 corpuscles than of their origin. 



The work of Wissozky is very interesting. This author began with the study 

 of the reaction of hemoglobin-bearing cells to eosin seen in drops of fresh blood. 

 From this he went on to making flat preparations of the embryonic membranes at 

 the edge of the placenta of the rabbit, fixed the membrane in toto, brushed off the 

 epithelium and stained the whole with hematoxylin and eosin. He made similar 

 preparations from the allantois of the chick and the rabbit, and described the forma- 

 tion of single angioblasts, which he called hematoblasts, described how they formed 

 a network with numerous processes which he interpreted as indicating amoeboid 

 activity, and, finally how vacuoles formed in these solid bands. Thus he says: 



"An irgend einer Stelle des soliden haematoblastischen Stranges erscheint zuerst ein 

 durchsichtger farbloser Streifen, welcher gewohnlich bogenformig ist; dieser Stfeifen 

 erweitert sich ferner, nimmt die Gestalt eines Halbmonder an, seine Enden nahern sich 

 melir und mehr, um endlich zusammen zu fliessen. Auf diese Weise entstehen in dem 

 Protoplasma der haematoblastischen Strange die beschriebenen Liicken, in welchen die 

 embryonalen Blutkorkerchen liegen, umgehen von durchsichtigen, farblosen Ringen." 



With his description he gives a beautiful figure of this vacuolation going on in bands 

 of single angioblasts, very like my figure 25, plate 5. 



All of the characteristics of angioblasts are beautifully shown in two figures 

 of Maximow (1909, plate xvm, figs. 1 and 8). These masses of cells (the first taken 

 from the area opaca of a rabbit embryo and the second from the forerunner of the 

 endocardium of the heart of a rabbit) show the azurophile cytoplasm and the tend- 

 ency to form syncytial masses. This is especially true in his figure of the fore- 

 runners of the endocardium. In the first figure are shown the irregular processes of 



