92 A. A. W. HUBRECHY. 
evident proof of this has been forthcoming (’02, Fig. 75, 7; 
77, h—k). 
Now considering the two facts (a) that the first source of 
the vasifactive tissue is always the entoderm, and (b) that 
the stalk necessarily increases in length with the growth of 
the embryo (yet more so in Tarsius than in monkeys and 
man, because in T'arsius it bends round towards the surface! 
of the blastocyst opposite to the embryo), then we cannot 
wonder that active entoderma! tissue is left behind in the 
stalk even when the rest of the intestinal wall undergoes the 
folding processes by which its definite tubular shape is gradu- 
ally brought about. ‘his entoderm, of which I have been 
able to follow even the very earliest apparation (’02, Figs. 
56, 57, 59—61) takes the shape of a tubular extension in the 
lengthening stalk. I have particularly called attention to 
the fact that it does not grow into the stalk actively, but that 
it has spun out (02, Fig. 11, a—c, Taf. XII) passively, as we 
saw was the case with the lengthening of the notochord 
(p. 37), and similarly with the thickening of the placenta 
(p. 125). 
It is not suggested here that, when once the connective 
stalk is thoroughly vascularised and the vessels carried by 
it have spread out on the inner surface of the placenta and 
have provided branching capillaries for the vascularisation 
of the embryonic placental villi, any further vasifactive pro- 
cesses go on or start from the endodermic epithelial tube, 
1 This expression should be understood cum grano salis. It is not the 
stalk that bends down, or has during its lengthening process bent down 
towards that opposite surface, but it is the embryonic shield that has, so to 
say, crept upwards (as I have elsewhere described [’02, p. 19; ’07, Figs. 
w3—w. |) along that surface of the blastocyst, which is opposite to the 
placental attachment (Figs. 62—65). The shield region is originally situated 
quite close to the surface of attachment; later, when the amnionfolds are 
being formed, it is found diametrically opposite to the latter. ‘This change in 
the situation of the embryo with respect to the placeuta does not occur in 
monkeys and man, hence the connecting stalk in their case is much shorter 
than in Tarsius. At the same time they have for this reason their backs turned 
towards the placenta, T'arsius, on the contrary, its ventral surface. 
