112 CARNEGIE INSTITUTION OF WASHINGTON. 



tissue extending into the cavity of the o\Tim. The stronger strands of 

 magma are accompanied more or less by mesenchjnne nuclei, showing 

 that the magma itself must be viewed as an independent connective 

 tissue identical with the mesench>ane of the chorion. As the amnion 

 extends, these strands are pushed aside and their final remnants are 

 seen in that portion of the exocoelom which encircles the umbilical cord. 



In pathological specimens the reticular magma increases in quantity 

 in the earlier stages of development, the increase continuing for a 

 number of months of pregnancy. Frequently the meshes between the 

 reticular fibrils are filled with peculiar stratified granules which take on 

 an intensive hematoxylin stain. Often the amnion is destroyed 

 early in development, and in this case the magma may dissolve; but 

 sometimes it increases greatly in quantity, fomiing a gelatinous mass. 

 Frequently, pathological ova are encountered in which the develop- 

 ment of the embryo is retarded, and the amnion is often found filled 

 with a flaky deposit that, as time goes on, increases greatly in quantity 

 and finally forms large crusts which invest the embryo. In other cases 

 there is a marked hydramnois, and in certain instances, in which the 

 amnion is destroyed, the magma dissolves, leaving only the embryo 

 floating in the fluid encircled by the chorionic wall. Specimens are 

 also found in which the cavity of the amnion is greatly enlarged and is 

 filled with a jelly-like substance, which in later stages may fonn crusts 

 encircling the embryo. The true relation between the pathological 

 changes of the contents of the exocoelom and of the cavity of the amnion 

 remains to be detennined. 



Professor Florence R. Sabin has continued her work upon angio- 

 genesis in the chick and the pig. The first vein of the embryo is the 

 duct of Cuvier, which forms a direct connection between the aorta and 

 the vitelline veins. The cardinal system in general arises as a longi- 

 tudinal system of veins from primary branches of the aorta. The 

 cardinal system proper extends throughout the zone of the myotomes 

 and lies in the Wolffian groove ventral to the myotomes. In the chick 

 the direct connection between the aorta and the heart occupies the zone 

 of the first three or four myotomes. Eventually the plexus of the 

 vessels representing the duct of Cuvier in the chick covers the zone 

 of the first seven myotomes. In the pig the posterior cardinal vein 

 develops from lateral branches at the same time as the nephritic 

 tubules, and these lateral branches alternate with the nephritic tubules. 

 In the chick the posterior cardinal vein develops more rapidly than the 

 tubules, and comes in part from lateral branches of the aorta, which 

 are intersegmental, but mainly from dorsal segmental branches, which, 

 however, do not grow first to the spinal cord, but rather directly 

 lateralward to the Wolffian groove, where they anastomose to make a 

 longitudinal vein. 



