68 A. A. W. HUBRECH'. 
in the posterior region of the annular zone described in 
Chapter II, paragraph 2b, and diagrammatically represented 
behind the protochordal wedge in Fig. 46. The fact that in 
and behind this entodermic proliferation Kupffer’s vesicle is 
developed seems to further confirm that homology, as will be 
noted below. This vesicle becomes apparent when the yolk 
has become quite enclosed by embryonic tissue. 
I have pleasure in noting that my identification of Kupffer’s 
vesicle in T'eleosts with the allantois in primitive mammals 
(a comparison which Kupffer himself did not fail to make) 
is accepted by Boeke. A comparison between Figs. 90, 
128, and 63 will further elucidate the chain of thoughts 
here implied. And I may call particular attention to Swaen 
and Brachet’s article (04) and their figures 58 to 77 (Pl. XV) 
of Trutta fario in order to show how these authors have 
established a close connection between this cylindrical posterior 
continuation of the entoderm, which goes by the name of 
Kupffer’s vesicle, and the production of vascular tissue (Swaen 
and Brachet’s Lame vasculaire, L.v.). I invite close com- 
parison with what I have written about Tarsius on p. 45, 
and with Fig. 102 which was given of that mammal, and 
have no doubt that if we compare Kupffer’s vesicle not with a 
free allantois of reptiles and most mammals, but with the 
incipient allantois met with in Primates, many apparent 
objections to such comparison will fall to the ground. 
Summary or CuHaprers I anp II. 
Before the ectoderm and the entoderm have become differ- 
entiated from each other there is in mammals a distinct Jarval 
cell-layer surrounding (as soon as the cleavage of the egg has 
attained the morula stage) the mother-cells of the embryonic 
tissues. This layer, to which the name of trophoblast has 
been given, and which is, phylogenetically, an ectodermal 
derivate, contributes towards the formation of chorion and 
amnion, and is shed at birth. The mother-cells of ecto- and 
entoderm enclosed within the trophoblast, and at one point 
