228 
KlCHAKl) ASSHETON. 
segmenting egg of tlie sheep. Moreover, the growth round 
would seem to be in the opposite direction to that required 
by the hypothesis. As I have said on a former occasion 
(^08), “van Benedeu is also a little inconsistent, for in his 
former papers on the rabbit he shows that the epibole is in 
the opposite direction to that required by his newer hypo- 
thesis. In 1880, in his description of the rabbit, he describes 
the epibole as occurring in such a way as to place the inner 
mass at the point where the enveloping rim coalesces (vide 
van lieneden, ’80, fig. 7, fig. 5^^'), and marks the spot where 
the embryonal area will eventually be.” 
Tlie third alternative I still believe to be the most com- 
pletely consistent explanation of the early stages of the 
development of Eutherian mammals, and so strongly do I 
believe in it that I would urge the development of the sheep 
and bat as strong evidence against Hubrecht’s attempt to 
destroy the old group of Amniota. 
This third alternative (p. 22G) accounts (1) for the epibole 
by regarding it as a feature peciiliar to Eutherian mammals 
and due to an overflow, as it were, of the yolk or hypoblast 
cells over the epiblastic rudiment, which, as the centre 
whence the great bulk of the animal will be formed (for it 
includes the whole of the secondary growth centre), is bound 
to l emain inactive. 
(2) F or this lethargic state of the epiblastic mass continuing- 
through many days, until the space necessary for development 
of the embryo, on the old Sauropsidan egg type, has been 
provided. 
(3) For the sharply marked off character of the epiblastic 
mass. 
(4) For the frequent protoplasmic connections between the 
inner layer of the inner cell mass and the blastocyst wall. 
(5) For the fact that cells of the inner mass pass into the 
outer cell wall (Assheton, 1908). 
(6) For the rejection by the embryonal area of cells of the 
trophoblast layer. 
Lastly, it may be said that the theory demands no change 
