Embryonic Development in Man. 399 



condition of congestion and glandular hypertrophy, the ovum pro- 

 duces necrobiosis ot coagulation necrosis in the structures of the 

 mucosa. At the same time the trophoblast exhibiting great pro- 

 liferative energy now penetrates through the necrotic tissue, into 

 the connective tissue of the mucosa. Here the phenomena of edema 

 and of a violent hemorrhagic inflammation are now established. 

 Veins and capillaries become enormously dilated, the blood current 

 becomes sluggish, edematous infiltration becomes pronounced. The 

 ovum automatically orients itself, so that the embryo comes to be 

 situated towards the muscularis. The proliferating trophoblast with 

 its syncytium, provided with cilia or rods, at this time begins to 

 break into and to open up dilated maternal capillaries. Maternal 

 blood now makes its way into the trophoblast, whether it here finds 

 preformed cavities or whether it forms these cavities in a loose 

 protoplasm in consequence of hydrostatic pressure, we do not know. 

 While the trophoblast opens up the enlarged maternal blood lacunae, 

 the hypertrophy of the mucosa, as a whole, goes on. The gland 

 spaces become large and cystic, their ducts lead to the surface in 

 a tortuous manner. A separation into a spongiosa and compacta 

 becomes early established, and in the latter some cells early assume 

 a marked decidual character. 



The ovum is now interstitially embedded in the mucosa and sur- 

 rounded by a border zone which is composed of an admixture of 

 still attached or detached trophoblast elements, degenerating fixed 

 maternal cells, both connective tissue decidual cells and glandular 

 epithelia. In this border zone (^'Umlagerungszone") are also con- 

 tained enormously enlarged maternal blood vessels, cystic blood-filled 

 gland spaces and free blood. The ovum almost floats as it were 

 in a lake of blood partly contained in the trophoblast cavities, 

 partly in the cystic maternal gland spaces, partly freely infiltrating 

 more or less all of the tissue in the direct neighborhood of the 

 growing germ. 



When the preliminary paper was read in Boston, Mass., Au- 

 gust 20, 1907, before the Section on Embryology of the Seventh 

 International Zoological Congress, Professor A. A. W. Hubrecht, 

 the Chairman of the Section, in the discussion of the paper, called 



