454 JOHN LEWIS BREMER 



trace of angiocysts, nor are there even vacuoles in the cell proto- 

 plasm. The cells forming it are broader, or thicker, than the 

 surrounding mesenchjniial cells, many of which are spindle-shaped, 

 and the cord cells usually lie in well defined, though small, cavities 

 anlong the mesodermal fibrils and cell processes (fig. 5). 



The yolk-sac of the Herzog embryo is covered by a mesothelium, 

 apparently originally complete, though broken now in many places 

 but this mesothelium lies everywhere close against the enclosed 

 entoderm, and shows no signs of the funnel-shaped ingrowths 

 such as are found around the body-stalk. In Jung's paper, how- 

 ever, (his fig. 17) the mesothelium of the yolk-sac is shown as quite 

 far separated from the entoderm, and in at least two places in the 

 one drawing (the only section of the embryo proper figured by him) 

 the mesothelium of the distal pole is arranged in what appear to 

 be typical funnels. 



In the Bryce-Teacher ovum, which was also most generously 

 placed at my disposal for examination, the mesodermal cells are 

 often spindle-shaped, and may be arranged in chains of two or 

 three cells, followable from one section to another. But on recon-' 

 struction these cells do not form a net, except by the very finest 

 protoplasmic processes, as in ordinary mesenchyma. A coelom is 

 absent, and therefore there is no mesothelial surface. Though 

 the chains of cells look somewhat like angioblast cords, I am satis- 

 fied that they are only portions of the general mesenchyma, 

 especially since similar chains of spindle-shaped cells, followable 

 for only short distances, and not connected with the vascular net, 

 are to be found in the mesenchyma of older embryos, even at the 

 time when the blood-vessels are well established. Much larger, 

 more distinct cords of cells in the mesoderm of this ovum are 

 found to be processes of the surface ectoderm, of which a few cords 

 traverse the mesoderm of the future chorion. Similar, but hollow, 

 "chorionic canals" are described by Grosser and by F. T. Lewis^" 

 in older embryos. From my study of this ovum I should say that 

 no vascular anlages exist at this stage. 



><> Lewis, F. T. Communication to the 30th Session of the Am. Ass. Anat., 191.3. 



