22



M. M. Aubey,



prominent and relatively enormous orbits, the rest of the body

forming a still shapeless mass recognisable as the beginning of the

blood-vessels ; the whole is contained in a very fragile vitelline mem¬

brane.



The Embryo from the Eighteenth to the Twentieth Day.


Growth is rapid at this period ; the alimentary reserves are

massed in a pouch outside the umbilicus and linked to it by a

pedicle traversed by nutrient vessels. The head is formed, and the

whole is surrounded by an envelope full of a yellow fluid strictly

comparable to the amniotic fluid of mammalia; this is the germinal

vesicle which is developed, thanks to the vitellus. Macroscopically

the egg reveals a mass swimming in the midst of white and yellow

fluid. It is at this period that the mortality of the embryos is

greatest.



The Embryo from the Tiventieth to the Thirtieth Day.


Mortality is rarer at this stage ; the embryo is a little more

developed; in every case it possesses all the organs which are

essential. The head is well formed, as are also the limbs, which have

claws and even scales in the lower parts; the beak is still soft,

though defined. The vitelline membrane is richly nourished,

increasingly so as one approaches the nutrient zone; the external

vascular network sends out slender branches, which thicken at the

level of the air-chamber to allow greater aeration of the blood.


The Last Days of Incubation.


The well-developed embryo completes its organisation and

begins to move. Its shadow, of the greatest value, allows one to

follow its progress.


The skin is folded, especially at the level of the limbs. The

head is truncated; the body is clothed with down rolled into tubes,

which at birth give it the appearance of a Hedgehog. The abdomen

is retracted, all the nutritive vitelline mass being outside and

attached to the umbilicus by a large vascular pedicle. The vitelline

membrane is thickened and provided with great blood-vessels, whose



