DEVELOPMENT OF THE CHICK. 3 



rransparent. \Yithin the white lies the yolk, surrounded by a .sliglit membrane, which serves 

 to guard it from mixing with the white. In order to prevent the yolk from shifting its place at 

 every change of position in the egg, it is anchored, so to speak, in its proper place by two 

 curious ligaments fastened to the yolk membrane. Upon the yolk, and immediately under 

 the membrane, lies the little genu which in the space of three weeks will be developed into a 

 bird. 



After a few hours of warmth, the first idea of the chick is seen in a little whitish streak, 

 barely one-tenth of an inch long, rather wider at one end, and always lying across the egg. By 

 degrees, this streak enlarges, and forms a groove between two little ridges, and in a few hours 

 later, a delicate thread is seen lying in the groove, being the first indication of the spinal cord. 

 Presently a number of the tiniest imaginable square white plates make their appearance on 

 each side of the thread, and are the commencement of the vertebrfe. It is most curious to see 

 these gradual changes, for the different parts come into view as though they were crystallized 

 from the substance of the egg. By the end of the first day the germ takes a curve, and looks 

 sometliing like a little maggot as it lies in the yolk. The little heai-t is just jjerceptible on the 

 second day, and on the third a series of blood-vessels have been formed, and are supplied with 

 blood by a very curious system of arteries and veins. Bj' similar processes the various organs of 

 the body are built up, the feathers beginning to make their appearance about the twelfth day, 

 and on the nineteenth or twentieth day the chick pierces with its beak the air-sac which lies 

 at the blunt end of the egg, and by means of the air which it thus obtains is often able to 

 chirp before it chips the sheU. 



Duiing this period of its existence the young bii'd is nourished by the yolk, which is con- 

 nected with its abdomen, and which is not separated from the body until the chick has broken 

 the shell, and is able to respire freely. When leaving the egg-shell, the chicken pecks in a 

 circle, which nearly corresponds with the shape of the air vesicle, so that when it emerges it 

 walks out of a circular trap-door which it has cut for itself, and which often remains suspended 

 by a hinge formed fi'om an uncut portion of the lining membrane. It is j^ossible that the 

 shell may be softened in this spot by the presence of internal air, and may therefore afford an 

 easier passage to the inclosed chick. In order to enable the tender-billed little creature to 

 penetrate so hard a substance as the egg-shell, the tip of its beak is furnished with a strong, 

 horny excrescence, which falls off shortly after the chicken has emerged from the egg, thus 

 carrying out the principle that nature abhors a supei-fluity. 



Having watched the little bird through its life-development, we will now proceed to a 

 short examination of the bird-skeleton, and will take for an example that of the eagle. Even 

 in the mammalia the skeleton presents an appearance very different from that of the living 

 creature, and in many instances the external structure and its bony framework are so unlike 

 each other that an inexperienced observer would probably refer them to different animals. 

 But in the birds the contrast is still more strongly marked, for the skeleton is not only 

 deprived of its fleshy covering, but also of the feathery coat which surrounds the bird so 

 thickly, and Avhich in many cases, such as the owl, entirely masks the general outline of the 

 bird. Taking the skeleton of the eagle as a good example of the bony scaffolding which 

 supports the vital and locomotive organs of birds, we will begin with the head and proceed 

 gi'adually to the tail. 



The chief and most obvious distinctive feature in the skull of a bird and of a mammal 

 Ues in the jaw-bones, which in the bird are entirely toothless, and are covered at their extrem- 

 ities with a peculiar homy incrustment, termed the beak or bill. This biU is of very different 

 shape in the various tribes of birds ; being in some cases strong, sliai-p, and curved, as in the 

 birds of prey ; in others long, slender, and delicate, as in the creepers and humming-birds ; 

 and in others flat, spoon-like, soft, and sensitive, as in the ducks. The movement of a bird's 

 jaw is not precisely similar to that of a mammal, owing to the manner in Avhich a certain 

 Uttle bone, termed from its squared shape the quadrate bone, is articulated to the bones of 

 the skull. 



Passing from the head to the neck, we find a marked distinction from the mammals. In 

 them, the vertebrae of the neck are never more than seven in number ; the long neck of the 



