Processes that flow at development of embryo are possible to compare with building of houses or fortresses, as from the outer world an embryo is shut off by a strong wall - shell. Material and life energy are needed for building of house. High molecular organic compounds - squirrel, carbohydrates and fats are building material for an embryo. It is "ore" from that a growing organism ladles building bricks the family, foremost amino acid and sugar, to build own albumens and carbohydrates from them. Carbohydrates and fats are a fuel. Oxygen that acts to the embryo through pores in a shell is needed for their incineration. But it is yet not all. "Building slags" and wastes appear from incineration of fuel are poisonous for an organism nitrous substances and carbon dioxide in the process of construction of body of embryo. They must be deleted from a growing organism and its direct surroundings. Nutritive in advance provide oneself in an egg: yolk, essentially, - a pantry with food supplies. As far as development of embryo yolk is expended so actively, that from him to the moment of hatching of nestling nothing remains almost. So, the problem of energy and building materials is decided. There are other embryonic shells in the eggs of birds. This shell a developing embryo becomes overgrown with thin tape, as plugs him in itself, and filled by the special liquid. How does oxygen get to the egg? And as does carbon dioxide hatch from it? All is surprisingly careful thought out here, to the little things. A shell is pierced by numerous narrow tubes. Pores are thousand in the egg; through them the interchange of gases comes true: oxygen acts, carbon dioxide leaves. But it is yet not all. Quickly to deliver acting on pores oxygen to fabrics of growing embryo, the special respiratory organ look like a placenta for mammals is formed in an egg. But it is another problem: how to deliver water to the embryo? It is needed for his formed fabrics and an embryo cannot normally develop without it. Different animals decide this problem differently. The eggs of snakes and lizards absorb water from soil. Thus an egg increases in a volume in 2-2, 5 times. But for lizards and egg snakes covered by an elastic fibred shell, for birds they are bound in the armor of shell. Development of embryo flows in the ball of contradictions and problems. Safe realization of new life is truly unbelievable process sliding on a razor-blade, between two abysses. The decision of one problem generates other here.
|