38 
The Illustrated Book of Poultry. 
at length a large portion of the space within the shell, the egg itself drying up in proportion. 
eggs on the point of hatching it usually occupies about one-fifth of the space. It has been 
conclusively proved by experiments that the perforation of this air-chamber, even by a needle- 
point, is an effectual prevention of successful hatching. 
In the last portion of the oviduct the egg becomes coated with that calcareous deposit 
which forms the shell, after which it passes into the cloaca and is ready for expulsion. In some 
breeds colouring matter is added to the solid ingredient, producing the deep-coloured eggs of the 
Cochin, and in other birds the splashed and spotted patterns so well known. In fowls which 
lay coloured eggs similar splashes often occur, and we have had Brahma hens which laid eggs 
with a white ground, covered thickly over by chocolate-coloured spots. We have had others, 
again, lay eggs covered apparently with a coat of whitewash, which on being rubbed off with 
a rough cloth revealed the usual buff-brown tint beneath. All these things obviously depend 
on some peculiar condition of the secreting organs, as does the shape of the egg of each bird 
when finally laid. 
Many occasional departures from the ordinary type of egg will now be readily understood. 
If the latter portion of the oviduct be in an unhealthy condition, or if yolks be matured 
by the ovary faster than shells can be formed by that organ, “ soft ” or unshelled eggs will 
be produced. If, on the contrary, the oviduct and its glands be active, while the supply of yolks 
is temporarily exhausted, the diminutive eggs, which consist only of white and shell, and which 
not unfrequently terminate the laying of a long batch, may be expected to occur. Any 
inflammation of the middle portion of the passage will result in eggs without even the membranous 
skin ; and if the entire canal be in an inflamed condition, yolks alone will probably be dropped 
without any addition whatever, even of white. This last occurrence therefore always denotes 
a very serious condition, and should be met at once by depletic medicines, or it will probably 
be followed by the loss of the bird. 
As we have already remarked, the white forms the principal nourishment of the chick whilst 
within the egg ; and we repeat this because it is the very opposite of the popular idea. Many 
writers who ought to know better have stated that the yolk furnishes the food of the chick, whereas 
the fact is that up to about twenty-four hours before hatching the yolk suffers hardly any 
diminution. At about that time it begins to be absorbed through the umbilicus or navel into the 
abdomen of the chicken, and is in fact a wonderful provision by which the newly-hatched little 
animal is supplied gradually with the most highly nutritious food during the earlier stages of its 
existence. Traces of the yolk may be found by dissection in the abdomen of the chicken even 
after ten days have elapsed ; and in chickens just hatched much is often net fully entered within 
the abdominal cavity, and can be plainly seen with the naked eye. 
We have no space to enter fully into the different stages of development of the chick during 
the period of incubation, but must confine ourselves to a description of the first, middle, and 
final stages of the process. When the egg has been sat upon or placed in an incubator for a few 
hours, the size of the germ can be seen to be sensibly enlarged ; and before the expiration of 
twenty-four hours small blood-vessels can be seen round it, which under the microscope present 
the most beautiful appearances which can be imagined. About the third day a membrane 
called the allantois, and the purpose of which is to supply to the blood of the chick the 
oxygen which it obtains through the shell from the external air, begins to envelop the entire 
organism, and the egg presents somewhat the appearance of Fig. 18. At this period the chicken 
appears as a small gelatinous mass, of a nearly blood-red colour ; but the rudiments of the 
head and limbs can be easily discovered by careful examination. By the end of the tenth day 
