452 JOHN LEWIS BREMER 



stalk further toward the yolk-sac, and to follow one cord in its 

 tortuous course to its junction with the yolk-sac net. Other cords 

 from each net are apparently reaching out toward the other, some 

 having nearly spanned the intervening space (fgs. 2 and 3). 

 There are no cords unconnected with either net, such as are found 

 in the Minot embryo. The end of the chorionic net nearest to the 

 yolk-sac is composed of cords and unlined spaces, with no endo- 

 thelial angiocysts. 



A careful study of the unlined spaces in this embryo leads to 

 more convincing proof that they and the mesothelial ingrowths are 

 actually connected. In the Minot embryo such connections can 

 be made out only by reconstructions, whereas in the Grosser 

 embryo the plane of section has fortunately, in several instances, 

 shown the whole connection in a single section, as shown in figures 

 6 and 7. Cells resembling young blood corpuscles may be very 

 infrequently found in the unlined spaces, and even in the meso- 

 thelial ingrowths. 



The blood-island described by Grosser as lying in the mesen- 

 chyma of the body-stalk of his embryo, is found to be connected 

 by a protoplasmic cord, resembling an angioblast cord, with the 

 vascular net (fig. 2). In the Minot embryo a few smaller but 

 otherwise similar groups of cells are found, one of which is shown 

 (fig. 1) connected directly with an inpocketing of the mesothelium. 

 In both embryos the cells of the islands are rather small, rounded, 

 with little protoplasm, resembling in these respects the cells of 

 the young islands of the yolk-sac. In the body-stalk of the Dandy 

 embryo though it is much older than the two under considera- 

 tion, I have found similar islands, one directly connected with 

 an inpocketing of the mesothelium but not with the blood- 

 vessels, the other smaller one, of about 20^ in diameter, with no 

 present connection with either blood-vessel or mesothelium. 



In the embryo described by Professor Debeyre which he also 

 most kindly allowed me to examine, the relations of mesothelium, 

 unlined spaces, cords, angiocysts, and blood- island appear to 

 be the same; but no reconstructions were made. 



Herzog, it will be remembered, described in his embryo certain 

 rings and small groups of cells, lying iii the coelom at the edge of 



