186 A. A. VV. IIUBRECHT. 



bined with a penetration of the whole bhistocyst inside the 

 maternal tissue, e.g. man, anthropomorphae, hedgehog, Gyra- 

 nura, and many rodents. This was naturally a far higher 

 position of vantage than any peculiar fixation inside the 

 lumen of the uterus, for now, when once the blastocyst was 

 encapsuled inside its mother's tissues, it could be most 

 thoroughly bathed iu maternal blood without any extravasa- 

 tion into the uterine lumen. To take three examples of this 

 we may allude to the guinea-pig, the hedgehog, and man. 

 Still, all these utilise the favourable conditions offered to them, 

 thauks to their situation inside a capsula or decidua capsularis, 

 in a very different manner. 



There is a most remarkable amount of similarity between 

 the hedgehog and man, as far as the conditions are concerned, 

 which the mother olfers to the young. But then the embryo 

 itself of man has seen its way to much more intense utilisation 

 of these favourable conditions than the hedgehog embryo has. 

 Principally because the vascular system of the hedgehog 

 develops iu a sequence of stages, which serve to bring its 

 area vasculosa on the umbilical vesicle in primary contact 

 with the profusion of maternal blood by which the blastocyst 

 is surrounded. 



On the contraiy, in man this area vasculosa on the umbilical 

 vesicle is not in contact at all with the maternal circulation. 

 In man it is more devoted to hgematopoietic functions, i.e. 

 to the formation of new blood-corpuscles for the embryonic 

 circulation. But in another respect the human blastocyst has 

 got far ahead of that of the hedgehog, in so far as the de- 

 veloping embryo has succeeded in vascularising its outer 

 larval layer, its trophoblast, at a quite exceptionally early 

 moment, without the aid of any allantoic outgrowth, and 

 simply iu consequence of a very early segi-egation of certain 

 portions of the mesoblast, into which the entoderm sends both 

 blood-vessels and blood-corpuscles. This very early vascula- 

 risation of the trophoblast leads to a most intense osmotic 

 interchange between the blood of mother aud child — far more 

 intense that what obtains in the hedgehog, where an ompha- 



