226 
ItICHAED ASSHETON. 
(3) A growtli over the temporarily lethargic epiblastic 
mass by the yolk or hypoblast cells (Minotj myself). 
'I’he last two interpretations pi’e-snppose a derivation of 
the Eutherian mammal from Sauropsidan-like ancestors with 
large-yolked eggs. 
All these are plausible theories, and it would have been 
very interesting to have had Hubrecht’s opinion upon them, 
especially as the last two are completely opposed to his own 
views. Incidentally Hubrecht, in connection with the forma- 
tion of the cavity of the blastocyst, says (p. 6), “ E. van 
Beneden has ascribed the origin of the free .space between 
the epithelial outer layer and the inner mass to the extension 
of intra-cellular vacuoles (’9d). His interpretation has found 
no support in the results obtained by Keibel and myself, nor 
in those of Selenka for the opossum.” 1 should like to say 
thfit as far as my experience goes the cavity of the blastocyst 
appears to arise, as van Beneden says, as the extension of 
inti’a-cellular vacuoles in the pig and ferret, less clearly so in 
the sheep (and from general appearance of later stages still 
less in the goat), while in the rabbit it would seem as 
distinctly to be intercellular. 
Perhaps there is not very much in it, but so far as it goes, 
if the origin of the cavity is intra-cellular rather than inter- 
cellular, it tends towards the probability of the cavity in 
question being a vacuolation in a yolk bearing syncytium 
like the germinal wall of the Sauropsidan egg rather than a 
space between “embryonic” cells and an “ Embryonalhiille ” ; 
that is to say, it supports the last theory of the three suggested 
better than either of the other two. There can be no doubt 
tliat there are in the sheep, pig, ferret, goat (Assheton, 
’08, fig. 5), strands of protoplasm which connect the inner 
lining of the inner mass to the wall of the blastocyst, and 
this tends to sliow that the inner lining of the inner mass is 
of common origin with the wall of the blastocyst; that is to 
say, the hypoblast and trophoblast are one. 
With reference to the three diagrams on pages 229, 231, 
233 of my paper referred to above (’08), 1 fear I have not 
