EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 93 
which represents in this stalk what will in other mammals 
and in the Sauropsida be the inner cavity of the allantois. 
This epithelium is only a remnant of what has in earlier 
stages been a proliferating vasifactive region of the endoderm, 
and which, after being yet active for some time (’02, Fig. 61, 
65, 66), finally lapses into the position of a residuary structure 
ending blindly and being in the umbilical cord of the later 
foetal stages only difficultly recognisable as a string of cells of 
quite a rudimentary character. 
We have now followed the connective stalk of arsius and 
the endodermic epithelial tube within it, which we will call 
allantois, in its entire development. It is, in the present 
state of our knowledge, no unfair assumption to say that 
the genesis of the connective stalk of man and monkeys, 
with its epithelial entoderm tube, which there also is desig- 
nated as allantois, must correspond in its principal charac- 
teristics with what we have just described. And we may now 
emphatically affirm that the Primates have no free allantois, 
but that the stalk-like connection between embryonic shield 
and embryonic envelope is of so early a nature,and can be so 
perfectly explained without having resource to any ento- 
dermic outgrowth, that we are justified in looking upon this 
peculiar arrangement of the connective stalk of the Primates 
as more primitive than the free allantois of any 
other of the higher Vertebrata. 
Now let us for a moment try to realise how those who take 
the free allantois as the more primitive have to picture for 
themselves the phylogenetic origin of it. I have elsewhere 
(07, p. 58), in discussing this question, expressed myself 
as follows :—‘‘ We could not possibly imagine that the allan- 
tois arose as an independent vesicle spontaneously growing 
out from the hind gut. At what stage of phylogenesis would 
this have been inaugurated ? Has ever any amphibian-like 
animal been struck by the happy thought that it might allow 
its urinary bladder to undergo aso much earlier development, 
in order that it might obtain aso much more considerable 
size and such a copious vascularisation ? And that in this 
