Cuap. II. ABSORPTION OF THE ALBUMEN. 515 
the embryonic dise is sharply defined, not only the same homogeneity, but also 
We would 
this fact again, in order to allude more directly to the similarity in the conduct 
the same size, that obtained when they were in the ovary. recall 
of the yolk mass in the oval eggs of Cinosternoide with that of the families 
which have globular eggs. 
Immediately after the embryonic disc has become sharply defined, we per- 
ceive a remarkable change in that portion of the yolk mass which lies just 
below. the embryonic area“ (Pl. © 9b, fig: 1) a’, 4; a’; 4a, at, 5, a; Pl. II, fig. 
la). At this spot, a small quantity of clear fluid makes its appearance. Below, 
it rests on the great mass of yolk, (y,) and above, presses against the under-side of 
the embryonic dise (e) and its continuation, the germinal layer. Seen from above, 
the space which this fluid occupies appears dark, unless light is admitted through 
the side of the ega; 
go; but in profile it is as clear as glass. 
This, however, is 
not seen very readily, unless the slightly opaque germinal layer that surrounds 
the whole egg is broken through. The embryonic disc is also rendered more 
distinct and conspicuous by the presence of this dark background. At the same 
time, a slight enlargement of the yolk sac is noticeable. From these facts, we 
at once infer that the clear fluid under the embryonic disc does not arise from 
a liquefaction of a portion of the yolk mass, but that it is introduced from 
without, and is the cause of the increase in the size of the yolk sac. We are 
confirmed in this belief when we look at that portion of the albumen which 
overlies the embryonic area,’ and there find that a more or less circular portion 
1 The manner in which the albumen is absorbed 
into the yolk sac in the eggs of Birds seems not to 
have been observed with sufficient care. This pro- 
cess is very peculiar, and stands in direct relation to 
the embryonic area, and to the increase of the yolk 
sac. Nothing is easier than to ascertain the pre- 
cise amount of albumen that is absorbed into the 
yolk at successive periods of incubation, and the 
changes of form which the yolk sac undergoes in 
consequence of this absorption. It is only necessary 
to boil the eggs slowly, when the albumen discloses 
at once the changes it has undergone. Its absorption 
is at first distinctly circumscribed to the area above 
the embryonic disc; and the limits within which it 
takes place are so sharply defined, that, when the 
albumen is hardened by heat, there may be seen, 
above the growing germ, a hollow, truncated cone, 
(Pl. 9d, fig. 5,) the broad base of which is turned 
65 
towards the shell, while its truncated apex, turned 
towards the yolk, corresponds in width to the diame- 
ter of the embryonic disc. As the embryo increases, 
the cone appears gradually flatter and flatter and 
more truncated, until the broad embryonic dise oecu- 
pies the whole space in the upper part of the egg 
immediately below the shell membrane. The changes 
which the form of the yolk sac suecessively under- 
goes are not less characteristic: at first spherical, it 
is gradually more and more flattened within the limits 
of the embryonie area, until, by the time the area 
equals the diameter of the yolk sac, it is very nearly 
hemispherical, the flattened side being only slightly 
raised in the centre. I intend to publish, on another 
occasion, a series of drawings representing these in- 
teresting changes, as observed in hens’ eggs; mean- 
while I would seriously call attention to these facts, 
as they show clearly that the changes which the albu- 
