THE EGG AiND DEVELOPMENT OF THE YOUNG BIRD 97 



outer and inner layers of the amnion, 

 where it gradually extends till it entirely 

 surrounds the growing chicken close to 

 the outer shell and membrane of the egg- 

 It is furnished with a beautiful network of 

 blood-vessels, extended under the porous 

 envelope of the egg, while at the um- 

 bilicus they are in connection with the 



SEVENTH DAY: ALLANTOIS. nl. MORE DEVELOPED. 

 Yolk-sac shown in connection with the navel. (Magnified.) 



young chick. The allantois, with its 

 capillary blood-vessels, thus serves as a 

 temporary lung by which the blood is 

 oxygenated from the outer air, the chick 

 not being able to use its true lungs till the 

 very eve of hatching. The allantois is 

 thus a structure of cardinal 

 importance to the life of 

 the growing chick." 



In a Canary's egg at 

 the seventh or eighth da\' 

 signs of downy-like feathers 

 are faintly discernible, and 

 a movement of the young 

 bird is often perceptible if 

 the egg is opened at about 

 the ninth or tenth day. 



Just before hatching " the 

 beak ruptures the membrane 

 which divides off the air- 

 chamber, and the bird for 

 the first time breathes air through the 

 lungs, after which the chick's blood gradu- 

 ally ceases to flow into the veins of the 

 allantois, which has completed its work, 

 and is no more needed." 



Finally the yovnig bird, by the force of 

 its rapid movements within the shell, 

 13 



breaks from its prison. The first part of 

 the thin brittle shell to chip is that toward 

 the thick end of the egg, with which the 

 tip of the beak comes in contact. The 

 constant tapping causes the shell first 

 to crack, then the fractured part rises 

 slightly with 

 the pressure 

 of the beak, 

 that portion 

 directly over 

 it dropping 

 off, and the 

 movements of 

 the young bird 

 gradually in- 

 crease the 

 crack round the 

 dom for the head, wings and legs to move, 

 and complete the young bird's escape. 



The arrangement of the young bird the 

 day before hatching is shown in the accom- 

 panying illustration, while the next diagram 

 shows the bird forcing its way from its 

 prison with the egg fractured half-way 

 round. The other part of this illustration 

 shows how the two portions of the shell are 

 forced apart as the young bird escapes 

 from it. 



NEARLY READY TO HATCH. 



egg, thus giving free- 



EGG FRACTURED BY 

 YOUNG BIRD. 



POSITION OF SHELL AFTER ESCAPE 

 OF BIRD. (.Magnifieil.) 



" During this process of development 

 the embryo has at first been lying as a 

 small object on the upper 

 surface of the yolk ; later 

 on, as it increases in size 

 and definiteness of form, it is clearly 

 apparent that the neck of the yolk-sac is in 



Nourishment 

 of the Chick. 



