even experienced zoologists with absolute certainty can not say exactly how many species exist today and existed before on this planet.Constantly open up new varieties, and the face of the Earth, unfortunately, the old species disappear.Perhaps that is why so important to know more about the reproduction and development of animals to try to artificially prevent the disappearance, to try to comprehensively examine standing on the brink of extinction species.
little about classification
Animal Kingdom has a lot of types and classes, including worms, molluscs, crustaceans and echinoderms, arachnids and insects.And to vertebrates listed as: fish, amphibians, reptiles, birds, mammals.A variety of animals living on the planet, are well represented viewports sets.But these are different in structure, animal united in one kingdom, differ in many respects.How to breed animals?Different groups of the process is carried out differently.Let's look at the basic types.
For some lower animals (invertebrates) is characterized by asexual reproduction is the easiest way to create and increase the offspring.Reproduction and development of animals of this kind carried out by means of direct fission or budding.These animals include worms, sponges, jellyfish, Amphioxus and many others.In fact, they are not so little.But the nature of the process of evolution has created and other, more time-consuming and complex process of reproduction.
This type requires two floors to create offspring: male and female.Reproduction and development of animals is done by laying eggs or eggs, calving (mainly mammals).For example, lay eggs and insects and arachnids, as well as snakes and birds.Spawn: amphibians and fish.But some species - viviparous (eg, guppies).They give birth to cubs and fed them milk all mammals (including man).In some species, reproduction occurs without the participation of males.This phenomenon is called parthenogenesis.Distributed by lizards and bees, for example.
It also takes place in different ways.So insects, for example, there are three stages: egg, larva, pupa, adult individual, able to lay eggs.And some fish reproduction and development of animals of this species occurs in the mouth of the female, where it bears eggs until the offspring.Amphibians from the egg develops an intermediate form - the tadpole of which already formed adult frog.Turtles and snakes offspring derived directly from eggs, like birds.All mammalian species are viviparous, even dolphins, which ranked as the ancient fish.They nurse their offspring milk, hence the name of the class.Maturation progeny in various animal species occurs at different times from a few minutes to tens of years.The most "fast" - from one-day butterflies and other insects.Most slowly maturing young generation - have a highly organized class of mammals.