UG 
laOIlAUD ASSHETON. 
Patterson is not iiltogetlier free from doubt, I venture to 
oifer the following notes by way of criticism, which may 
possibly, and I hope will be, successfully met. Briefly 
stated Patterson^s account is as follows: He denies that 
gastrulation in the pigeou’s egg occurs by delamination or 
any process of ingrowth from the germinal wall or other 
lower layer segments. Gastrulation, accoi-ding to him, takes 
place befoi’e the egg is laid by a process of involution of the 
outermost layer of cells of the segmented blastodisc. At the 
close of segmentation this outermost layer of cells, which 
forms a continuous membrtine, becomes detached from the 
sub-lying cells and yolk along that part of its margin which 
is towards the future posterior end, and the detached margin 
becoming involuted, grows forward as a thin free edge 
beneath all the loose cells which admittedly exist in the 
deeper parts of the segmented blastodisc. This free edge 
joins up in front aud at the sides with the wall of yolk that 
contains nuclei (i.e. the germinal wall), and forms a con- 
tinuous sheet of cells — the entoderm or hypoblast. As the 
subgerminal cavity expands it excavates the germinal wall, 
and a sheet of cells derived from the germinal wall is left above 
the cavity. To this sheet the “ iuvaginated ” entoderm fuses. 
Thus the gut entoderm is formed by involution and the yolk sac 
entoderm by excavation. The loose cells lying beneath the 
outer layer, now to be termed “ epiblast,” are said to pass 
into the outer layer, and so also to form part of the epiblast. 
'Jdiis involution process is said to be still further complicated 
by the concrescence of the lip thus formed giving rise to a 
linear seam — the future primitive streak, which is withdrawn 
later within the area pellucida by a sweeping round of the 
germinal wall in a manner reminiscent of Duval’s attempt to 
prove a process of concrescence at a time subsequent to the 
laying of the egg. 
CiuTiCAL Notes. 
It is claimed that this account of the formation of the 
entoderm or hypoblast by an infolding of the blastoderm 
