The form of living beings corresponds to their way of life and habitat – land, thing, soil. To keep in shape are:
* fluid skeleton – compression of the cavity fluid by contraction of muscle fibers. These are soft-bodied animals – worms, jellyfish, sea anemones.
* external skeleton – chitinous cover – insects, shells of molluscs, crustaceans
* internal skeleton – all vertebrates – fish, amphibians, reptiles, mammals.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.