The notion of ontogenesis. Ontogenes is the individual development of the organism from its inception to the end of life. One-cell bacteria and protogenics have a practical match to the cell cycle. It begins with the formation of a single-celled organism in the process of separation of the mother and ends with division or death.

In multi-cellary organisms, the beginning of a new organism is most likely to be the education of Zigos (sex multiplying) or the separation of descendants from the mother (sexless multiplication). Animals have two periods of ontogenesis, embryonic and post-embrione.

Embryonic, or foetus, the period covers the period between the first gig split to the egg or the birth of a young man. The embryo development of most animals is under a single plan and comprises three main stages: fragmentation, gauging and organogenes.

We'll look at the embryo development in the example of a primitive choired animal, a lounge (figure 83).

A number of consecutive mitotic tasks are under way after the fertilization of the winter. Cells that emerge, blades, don't dilute or increase in size. With every subsequent mith, they're getting smaller and smaller. This divide, which increases the number of blastomers without growth, is called Dragging. As a result of the fragmentation of the winter, the foetus becomes multi-cellary, with approximately the same volume.

When the jigos are fragmented, blastomers are sometimes disintegrated, of which separate organisms are subsequently developed. This is the form of mono-zigot twins, which are also referred to as single or identical.

The demise ends with the formation of a single-layer multi-celled foam, braces. In a typical case, it resembles a floor ball whose wall, formed by one layer of blastomers, is called blastoderm. There's a cavity inside the bladder filled with liquid, a blastockel.