Oocytes (eggs) is usually the embryonic form of an animal or egg. Oology, a special branch of zoology, is engaged in the study of them.
General information
Their sizes may vary. For example, in a mouse, the egg cell size is approximately 0.06 millimeters, but the diameter of the embryonic form of an African ostrich can reach 15-18 centimeters. The shape may also be different. But usually the eggs are spherical or oval in shape. In some living creatures, they can be oblong, elongated, as, for example, in mule fish, hagfish or insects. Depending on the degree of distribution and the amount of the nutrient inside the egg, the size and other characteristics are determined. The accumulation of the yolk (this substance) is carried out either in the form of a continuous mass, or in the form of granules. Depending on this, experts divide oocytes into different types. The fertilization process takes place in the upper part of the oviduct. In the course of passage of the oocyte through the canal, fragmentation occurs. This process proceeds according to the type of discoidal incomplete. Due to the fact that the beginning of crushing occurs already in the oviduct, in birds, a laid egg can stay on one ofstages of cleavage (like a pigeon) or gastrulation (like a chicken).
Bird egg
Females of all kinds of feathered representatives of the fauna lay oocytes. Different species lay eggs of different shapes. This is due to the place where the masonry will be located. For example, if the nest is arranged in holes or pits, then the eggs will be round. In birds whose clutch is located on rocky ledges, the oocytes will be oblong. Generally, the larger the bird, the larger the egg size. But there are exceptions to this rule as well. So, for example, brood species, whose offspring are immediately adapted to self-feeding, lay eggs that are larger (compared to the body of the female) than those whose chicks are born helpless. The ratio of oocyte mass to body weight in small species is often higher than in larger species. It is believed that the African ostrich lays the largest eggs. Relative to the body weight of this feathered representative, its oocyte is 1% of body weight. But the weight of a hummingbird egg is 6% of the weight of the bird.
Some structural features of bird eggs
In birds living in mountainous areas, oocytes have "ribs", like stiffeners. They are necessary to maintain the integrity of the eggs so that they do not break when the birds land in a nest that has a small area. It should be noted, among other things, that this rib is capable of withstanding pressures of the order of 40 kg/sq. see and the side where it isabsent - no more than 2 kg / sq. see. The surface of the eggs is rough or smooth, shiny or matte. The color can be absolutely anything: from pure white to green and dark purple. The surface of the eggs of some species is covered with speckles, in some cases forming a corolla around the blunt edge. The color will depend on the image and the nesting site. So, in many secretly laying eggs and domestic birds, the shell is white. For those who leave the clutch on the ground, the color becomes identical to the surrounding conditions: it merges with the pebbles or plant rags that line the nest. The egg receives its color even in the birth canal of the female. So, for example, biliverdin (pigment) in combination with zinc gives a blue or green color to the surface of the egg. Due to protoporphyrin, a red or brown color, or spots of such shades, is obtained. Next, let's take a closer look at the internal structure of a bird's egg.
Oocyte device
The structure of the bird's egg corresponds to the purpose. It contains everything necessary for the formation and development of a young organism. The embryo in the egg is nourished by compounds found in the yolk. This mass is presented in two forms - in white and yellow. They are arranged in concentric alternating layers. The yolk is enclosed in a vitellin membrane. It is surrounded by protein. In the early stages of shell development, bird eggs perform a nutritional function. Protein, in addition, provides protection for the new organism from contact with the shell. The contents of the oocyte itself are surrounded by twoshell layers: outer and inner. Considering the structure of a bird's egg, it is necessary to say a few words about the shell itself. It consists mainly of calcium carbonate. An air chamber gradually forms on the blunt edge of the oocyte after laying.
Yolk
Considering the structure of the bird's egg, the diagram of which is given below, it should be said that the deutoplasm (yolk) is an integral component of the internal contents of the oocyte. The yolk mass contains all the necessary substances that provide nutrition and normal development of the body. Deutoplasm is found in the egg not only of birds, but also of other animals (and in humans) and is an accumulation of plates or grains, merging in some cases into a continuous mass. The amount of yolk, as well as its distribution, can be different. With a small volume of deutoplasm, grains or plates are distributed evenly over the cytoplasm. In this case, one speaks of "isolecithal" eggs. With a large amount of yolk, the components accumulate either in the central region of the cytoplasm - near the nucleus or in the vegetative part of the oocyte. In the first case, they speak of centrolecithal, and in the second - telolecithal eggs. In accordance with the volume and degree of distribution of the yolk mass, the type of crushing of oocytes is also established. The chemical structure of the bird egg provides for three types of deutoplasm. The yolk can be carbohydrate, fat or protein. But, as a rule, in most individuals, the yolk components include, in addition to these compounds, mineralsubstances, pigments, ribonucleic acid, thus having a complex chemical structure. So, for example, in a chicken oocyte that has completed its growth, the yolk contains 23% neutral fat, 16% protein, 1.5% cholesterol, 11% phospholipids, and 3% mineral compounds. Different organelles are involved in the accumulation and synthesis of the yolk component: mitochondria, endoplasmic reticulum, Golgi complex. Synthesis of the protein component of the yolk structure in many animals occurs outside the ovary. Through pinocytosis, the protein component enters the developing egg.
Other elements of the oocyte structure
All shells prevent spreading, drying out and damage to the egg. But they do not provide the necessary moisture to the growing organism. It is formed by extra-embryonic organs. In particular, they include the water (or amniotic) membrane. Due to it, the amnion cavity is limited, which is filled with liquid, where, in fact, the body develops. Together with the water, two more layers are formed: vascular and serous (or allantois). In birds and reptiles, this layer is the organ of excretion and respiration. From the egg to the blunt and sharp edges of the egg, chalase depart - protein twisted dense strands. They provide a stable position of the core, preventing displacement from the middle position.
Shell
Studying the structure of a bird's egg, one should dwell in more detail on the layers surrounding the nucleus. The hardest outer layer is the shell. It is quite thick andperforms the function of protection against mechanical damage and the negative influence of the external environment. Under the shell there are shell membranes. At the blunt end, they diverge and form an air chamber. It contains oxygen, which is necessary for the respiration of a new organism.
Trophic oocytes
There is a type of eggs that serve as food for the offspring in the clutch. As a rule, they are unfertilized, and their appearance practically does not differ from ordinary ones. They are laid by females of some ants and termite queens until the colony begins to get enough food. In some cases, unfertilized oocytes of meat-egg and egg chicken breeds are also mistakenly called trophic, since they are used for food not by the birds themselves, but by humans and sometimes domestic animals.
