184 W. B. CHAPMAN 



these specimens. The effect of this irregular growth of the area 

 is apparently shown in th6 shape of the capillary plexus^thus, in 

 figure 13 the peripheral capillaries, formed by the breaking up of 

 the border vein, have grown out so rapidly that the inner capil- 

 laries have assumed a radial appearance. 



The general picture presented is shown in figure 3. The area 

 vasculosa appears, at first glance, to form a homogeneous net- 

 work of intercommunicating capillaries, extending from the em- 

 bryo proper to the border vein, which forms a wide rim around 

 the outside — (somewhat wider than shown in the illustration). 

 Examined more closely, it is noted that, anterior to the embryo 



Fig. 2 A diagrammatic sketch (actual size) of the blastoderm of an oper- 

 ated chick of 73 hours incubation, showing the distorted shape of the area 

 vasculosa. 



there is a depression in the border vein, behind which a vessel, 

 wider than most of the capillaries, extends toward the embryo — 

 the anterior vitelline vein. It is also to be noted that, in the 

 region surrounding the embryo, in the area pellucida, the spaces 

 between the vessels are larger than in the area opaca. One looks 

 in vain for any vessel which might be interpreted as omphalo- 

 mesenteric artery, or posterior vitelline vein. To the left of the 

 embryo there are two isolated blisters, and several blind ending 

 vessels. Fuller reference to this will be made later. 



Fig. 3 Camera lucida drawing of area vasculosa of an operated chick of 60 

 hours incubation (30 hours after operation). The capillaries in the area pellucida 

 have begun to break up. H, a hole torn in the blastoderm when mounting, X, 

 at this point the ink was forced out of the tiny vessels by too much pressure, and 

 settling in the tissues, so obscured the capillaries that they could not be distin- 

 guished. Veil. Vit. Anl., Anterior vitelline vein. 



