2 STRUCTURE OF THE EGG. 



another office, which is not possessed by hair or fur. They aid the creature in progression, 

 and enable it to raise and to sustain itself in the atmosphere. Towards the promotion of this 

 latter function the entire structure of the body and limbs is obviously subservient, and even in 

 the comparatively rare instances where the bird such as the penguin, ostrich, or the kiwi- 

 kiwi i s destitute of flying powers, the general idea of a flying creature is still preserved. 



The fuller and more technical description of the Birds runs as follows. They are vertebrate 

 animals, but do not suckle their young, nourishing them in most instances with food which 

 has been partially macerated in their own digestive organs, and which they are able to disgorge 

 at will, after a manner somewhat similar to that of the ruminating quadrupeds. The young 

 are not produced in an actively animated state, but inclosed in the egg, from which they do 

 not emerge until they have been warmed into independent life by the effects of constant 

 warmth. Generally, the eggs are hatched by means of the natural warmth which proceeds 

 from the mother bird ; but in some instances, such as that of the tallegalla of Australia, the 

 eggs are placed in a vast heap of dead leaves and grass, and developed by means of the heat 

 which is exhaled from decaying vegetable substances, and which is generated to such an 

 extent that in some cases, such as a wet haystack, it actually sets the seething mass on lire. 

 Urged by a like instinct, the common species of snake deposits its eggs in secret spots, such as 

 dunghills and hotbeds, and there leaves them to be hatched by the constantly generated warmth. 

 An analogous process has long been in vogue among the Egyptians for the hatching of young 

 poultry by artificial heat, and has been, in comparatively recent years, introduced into this 

 country. 



When the egg is first produced, the future chicken is merely indicated by a little germ- 

 spot, barely the size of a single oat-grain, and does not attain the power of breathing atmos- 

 pheric air, and receiving nourishment into its mouth, until a period of many days has elapsed. 

 To watch the gradual development of the young chick is a most interesting experiment, and one 

 which is full of suggestive instruction. There is but little difficulty in the matter, even in the very 

 earliest stages of incubation, for the structure of the egg is so wonderfully balanced, that in 

 order to view the little germ-spot it is only necessary to lay the egg on its side and remove 

 a portion of the shell, when the germ will be seen lying immediately under the aperture. In 

 whatever way an egg may be turned, the germ-spot invariably presents itself at the highest 

 point, provided only that the egg be laid on its side, and that the living principle has not been 

 extinguished, for life, however undeveloped, seems always to aspire. As the chick increases 

 in size, the manipulation becomes easier, but it is always better to immerse the egg in water or 

 other transparent liquid before removing the shell, and to keep it submerged during exam- 

 ination. 



There are few objects which will better repay investigation than the young bird in its 

 various stages of development. It is wonderful to see the manner in which a living creature 

 is gradually evolved from the apparently lifeless substances that are contained within an egg. 

 The being seems to grow under our very gaze, and we arise from the wondrous spectacle with 

 an involuntary feeling that we have been present at a veritable act of creation. To describe 

 fully the beautiful process in which a chick is elaborated out of the germ-spot would occupy 

 very many pages, and cannot be attempted within the compass of the present work. Briefly, 

 however, the order of events is as follows : 



When a newly laid egg is opened, it is found to contain a mass of substance which is 

 popularly divided simply into "white" and "yolk," but when examined more closely, by 

 placing it under water and carefully removing the shell, its contents are found to be very 

 elaborately disposed, so as to meet the object for which it was formed. Immediately within 

 the shell lies a semi-transparent and tolerably strong membrane, composed of two 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 sub- 

 stance, 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 



