HUBRECAT. Pl. Hi 
vat i fe 
§ 0, a vm 
: “oe tom 
Fig. 44—46. Three diagrams of the aspect of a longitudinal section 
through a Tarsius blastocyst. In Fig. 44 the trophoblast yet covers the embryonic 
ectoderm. The cayities of the umbilical vesicle (av) and of the extraembryonic 
coelom co in the ventral mesoblast entirely fill up the blastocyst; the connective 
stalk /c) is formed and it is at this spot (cf. Fig. 62) that the attachment of 
the blastocyst to the maternal tissue comes about. Ih Fig. 45 the embryonic 
ectoderm has become exposed to the surface after dehiscence of the trophoblast; 
the entoderm in the embryonic region has thickened. In Fig. 46 protochordal 
plate #f and protochordal wedge pw have become differentiated (cf. Fig. 48); 
under the stalk of ventral mesoblast the annular region of proliferating entoderm 
is once more cut longitudinally /@/; from here the vascularization of the con- 
nective stalk proceeds. — Fig. 47. The relative positions of ventral mesoblast 
(vm), trophoblast (¢~) on its way to leave the embryonic ectoderm uncovered 
(cf. Fig. 20) and umbilical vesicle in a stage of about the same age as the follow- 
ing figure. — Tie. 48. A somewhat later stage in which a distinet ventral 
proliferation (fw) of the ectoderm fuses with the entodermic proliferation (pf) of 
the entoderm. The protochordal wedge pw and the protochordal plate #p then 
become fused (cf. Tig. 52, 98, 99); the ventral mesoblast v7 springs from the 
embryonic ectoderm just behind the protochordal wedge. ¢r trophoblast, sm 
splanchnic mesoblast, 27 umbilical vesicle. 
