DEVELOPMENT OF THE CHICK. 3 



distinct layers, pressed closely to each other for the greater portion of its extent, but 

 separated at the widest end of the egg, and containing between the layers a supply of 

 atmospheric air to satisfy the requirements of the young chick. This space gradually 

 increases as the young bird becomes more developed. Within this membrane lies the 

 " white," a liquid, albuminous substance, which is also disposed in two distinct layers, 

 that which is nearest to the shell being rather thin and fluid, while the inner layer is 

 comparatively thick, tenacious, and very transparent. Witiiin the white lies the yolk, 

 surrounded by a slight 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 eo-a 

 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 

 germ 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 vertebrae. 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 something like a little maggot as it lies in 

 the yolk. The little heart is just perceptible 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. By 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 au- which it thus obtains is often able to chirp 

 before it chips the shell. 



During this period of its existence the young bird is nourished by the yolk, which is 

 connected 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 from an uncut portion of the lining 

 membrane. It is possible 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 superfluity. 



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 which 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 gradually to the tail. 



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

 lies in the jaw-bones, which in the bird are entu-ely toothless, and are covered at their 

 extremities with a peculiar horny incrustment, termed the beak or bill. This bill is of 

 very different shape in the various tribes of birds ; being in some cases strong, sharp, and 

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



b2 



