( 1081 ) 
The other specimens here figured are developmental phases in 
which the same separation between an outer trophoblast and an 
inner cell-mass is also visible. Three of them are instructive as 
representing yet different stages from fig. I—5. 
In fig. 6a-—-g sections are figured in which an inner ceilmass is 
apparently present. Close inspection shows that the cells whieh in 
fig. 6h—e appear to constitute an embryonic knob, at the same time 
form part of the outer surface of the biastocyst. Whether these very 
sections furnish arguments on which to conciliate HiLn’s interpretations 
with my own, must remain undecided for the present. Fig. 8 makes 
us acquainted with a blastocyst in which some two or three cells 
appear to be enclosed within an expanded trophoblast, but here again 
we may not look upon the specimen as decisive. 
Fig. 9a—d represent a stage just a little earlier than that of 
fig. 1—5. The enclosed cells are imbedded in a similar matrix and 
also number about sixteen. 
The size of the enclosed cells is intermediate to that of fig. 7 and 
1—5. The distinction between trophoblast and inner cellmass is 
equally evident. 
I finally mention, but do not figure, a somewhat later and considerably 
larger blastocyst, in which the cells that seem to represent the 
embryonic knob are histologically less perfect than those in fig. 1—4 
and might raise doubts whether this particular specimen is or is not 
a link in a normal developmental series. 
The facts which L have called attention to and which place us in 
the position of having to suspend our judgment with respect to 
fundamental support of Hirr’s theoretical speculations, prevent us 
a fortiori from weighing the respective merits of HiL1’s theoretical 
conclusions as compared to my own, and from entering into a debate 
such as he has opened in the article cited. It should not be lost 
sight of that just because the questions there raised are fundamental 
the discussions ought to be preeminently thorough and unprejudiced. 
The opposition with which my speculations on the first origin of 
the allantois have been met in different quarters is largely caused 
by that necessary sequel they lead to, viz. that no plausible phylo- 
genetic explanation of the ventral stalk of the Primates and of the 
free allantois of other mammals and of the Sauropsids is possible 
as long as we hold on to the line of descent which is so emphati- 
we know them), whereas in other cases these same cells undergo a certain amount 
of development within this wall and only later become intercalated among: the 
trophoblast cells in the way they do so variedly in numerous Eutheria. 
