90 A. A. W.. HUBRECHY', 
And so we must just recapitulate what we notice in Tarsius. 
The very small blastocyst of about ‘08 mm. diameter has 
only just become attached to the maternal uterine epithelium. 
That portion of its trophoblast which serves for the attach- 
ment proliferates considerably, and enters into firm union 
with the correspondingly proliferating trophospongia 
(Hubrecht, 799, Figs. 18, 55, 56). 
The blastocyst thus attached has only just passed through 
the phase (see p. 12) in which the trophoblast has opened 
out above the ectodermal shield (in a few cases I even found 
this process somewhat retarded: ’02, Figs. 49, 50). This 
shield is by no means situated diametrically opposite the point 
of attachment (Fig. 62), but on the contrary so as to bring 
the hinder end of the ectodermal shield in the most immediate 
vicinity of the place of attachment to the maternal mucosa 
(Hubrecht, ’07, Fig. w.’, w.”). From this hinder end 
of the ectodermal shield we have seen in a former chapter 
(p. 38) that the so-called ventral mesoderm proliferates 
backwards and downwards, at the same time becoming 
extended into a vesicle of extra-embryonic ccelom. In this 
vesicle the direct and axial prolongation of the original 
starting-point of the proliferation is encountered as a raphe 
of tissue, a thickened ridge of only a few hundredths of a 
millimeter in length. ‘his raphe is already in this very early 
phase the “ connective stalk ” by which the embryonic shield 
is Im communication with the proliferating trophoblast that 
inaugurates the placenta. There is not the least reason to 
look upon it as an eventual precocious segregation of anything 
like a free allantois ; it is early mesoblast, neither yet splanch- 
nic nor somatic by which the embryo is from the very 
earliest connected with that portion of the surface that is 
going to be the placenta. There is as yet no question of its 
being vascularised. And it is the method by which this 
vascularisation 1s going to be brought about which will show 
us the way to an interpretation of the allantois, quite different 
from that contained in the text-books. At the same time more 
satisfactory, because it is an explanation of the phylogeny of 
