514 EMBRYOLOGY OF THE TURTLE. Part III. 
in the outermost layers of this glairy substance has disappeared, and that the 
layers thus affected have shrunk toward the opposite side of the egg (Pl. 9b, 
fie. 3, a, 4, a, 5, a, 7, a). In this way the more interior layers of albumen become 
pressed against the shell, and the enlarging yolk sac on that side follows in 
their wake. In oval eggs, this absorption usually takes place at the side, mid- 
way between the two ends. Sometimes, however, when the egg is laid so as to 
rest in the nest with one end uppermost, the yolk mass shifts also, and the more 
buoyant portion, where the embryonic disc originates, faces toward the higher 
end of the shell; and here, too, the absorption of albumen first finishes: always 
above the embryonic disc, wherever it may be. In consequence of these changes, 
the centre of the yolk mass has not remained concentric to the outline of the 
shell, whether it be oval or spherical, and the layers of albumen appear propor- 
tionably much thicker on the under-side of the egg. It is very important to 
know that the absorption of albumen, and its infiltration imto the region below 
the embryonic disc, commence in the oviduct, and not after the egg is laid; 
as we are thus enabled to determine at what part of an oval egg the albu- 
men normally first enters the yolk sac. 
Upon carefully opening a Turtle from above without disturbmg the oviduct, 
it is possible to ascertain the exact position of every egg within the animal, 
and its relation to a horizontal plane. The embryonic disc, (that part of the 
egg which corresponds to the region of the cerebro-spinal axis,) is always next to 
the back of the animal. It is not, however, at all times situated at the high- 
est point of the egg, nor as near as possible to the back of the Turtle, but 
may be found now and then down toward the side of the egg (Pl. 11, fig. 4a). 
The longer axis of oval eggs is usually horizontal, and the shorter axis per- 
pendicular; so that, consequently, the longer curve of the shell is horizontal also, 
within the animal, excepting, perhaps, occasionally a slight elevation at one end, 
when the egg happens to be in a part of the oviduct which bends rather sud- 
denly upon itself. Now if, within the oviduct, the embryonic area is always situ- 
ated next to the back of the animal, it rests, of course, midway between the two 
ends of the oval egg, next to its longer curve, at what would naturally be called 
its side (Pl. 9b, fig. 1, 2, 2a, 3, 4, 4a). This, doubtless, is its normal position. The 
absorption of albumen normally commences above this point, as may readily be 
seen by opening Turtles just before the laying season. Therefore it is abnor- 
men undergoes are intimately associated with corre- tive substance accumulated around the yolk. On the 
sponding changes in the embryonic dise and in the contrary, these changes prove that the albumen is 
yolk sac, and do not take place in a manner to favor organically connected with the yolk, and performs a 
the idea that the albumen is merely a mass of nutri- regular function in the growth of the embryo. 
