Reproduction and development of animals. Materials for the lesson

Even an experienced zoologist scientist with complete certainty can not say exactly how many species of animals exist now and existed earlier on our planet. New varieties are constantly being opened, and from the face of the Earth, to great regret, the old species disappear. Probably, therefore, it is so necessary to know more about the reproduction and development of animals in order to try to artificially prevent this disappearance, to try to comprehensively study the species facing extinction.

A little bit about the classification

The animal kingdom numbers quite a few types and classes, among which are worms and mollusks, crustaceans and echinoderms, arachnids and insects. And the vertebrates include: fish, amphibians, reptiles, birds, mammals. The diversity of animals living on the planet is represented quite broadly by species sets. But such animals of different structure, united in one kingdom, differ in many parameters. How do animals multiply? Different groups have different processes. Let's look at the basic types.

Asexual reproduction

For some inferior animals (invertebrates), asexual reproduction is characteristic , as the simplest way to create and increase offspring. Reproduction and development of animals of this kind is carried out by direct division or budding. To such animals it is possible to carry worms, sponges, jellyfish, lancets and many others. In fact, they are not so few. But nature in the process of evolution has created another, more laborious and complex process of reproduction.

Sexual reproduction

This type assumes the existence of two sexes for the creation of offspring: male and female. Reproduction and development of animals here occurs by laying eggs or eggs, the birth of cubs (mainly mammals). For example, eggs are laid and insects, and arachnids, as well as snakes and birds. The eggs spawn: amphibians and fish. But some species of fish are viviparous (for example, guppies). Give birth to the cubs and they are fed by milk all mammals (including humans). In some species of animals reproduction occurs without the participation of males. This phenomenon was called parthenogenesis. It is common in lizards and bees, for example.

Development of animals

It also proceeds in different ways. So in insects, for example, there are three stages: the egg, the larva, the pupa, the adult individual, capable of laying eggs. And in some fish, the reproduction and development of animals of this species occurs in the mouth of the female, where it spawns before the appearance of the offspring. Amphibians from the eggs develop an intermediate form - a tadpole, from which an adult frog is already formed. In turtles and snakes progeny is derived directly from eggs, as in birds. All kinds of mammals are viviparous, even dolphins, which in ancient times were considered to be fish. They feed the offspring with milk, hence the name of the class. Maturation of offspring in different species of animals occurs at different times: from a few minutes to dozens of years. The most "fast" - for butterflies, ephemera and some other insects. The youngest generation, the slowest growing up, is in a highly organized class of mammals.