Oviparous and viviparous, and then there are also the oviviparous. Who they are and what they differ in we can perhaps remember from elementary school, or review it without dusting off the subsidiaries, right below. Each of these categories of vertebrates has its own reproductive strategy, and puts it in place to ensure that the growth and care of the embryo take place in the best possible way.
We aim for the best, it is normal, and we will see that the various species have selected the most convenient way for them. Are those silent magic of nature that leave you speechless but which you pay little attention to, often, because they are not very colorful in shapes and colors. But even science, with little effort, can become a source of amazement and admiration for the will to live expressed by each vertebrate which is on earth. Man including, but it is certainly not he who stands out in this discipline of wanting to live well.
Oviparous and viviparous: definitions
L'oviparity it is the reproduction strategy that sees the females lay fertilized eggs, then they continue their embryonic growth in an external environment, outside the maternal organism. Animals like almost all birds, numerous amphibians, insects and arachnids, many reptiles, fish, monotremes are oviperi. This type of reproduction, oviparity, differs from the other two - ovoviviparity and viviparity - because it is the only one in which development, called incubation, does NOT occur in maternal body.
There viviparity in fact, for example, it provides that the embryo remains inside the maternal organism while it grows, all the way. It happens both for many animals and for some plants, and it happens because the maternal body continues to nourish the embryo until its birth.
In eutherian mammals this occurs through the placenta, in the metaters in the uterus, but in this case the process lasts less and after a few days the fetus of a few cm reaches the breasts inside the pouch. Viviparous are above all i mammals and but in the category of viviparous there are some reptiles, some amphibian, as the salamander, and some species of arthropods and fish.
We have mentioned the plant world. Here i viviparous they are the specimens that “dress” the coast of the tropical marine coasts or those that live in areas that are periodically submerged by the tide.
In theovoviviparity, as for i vivipers, reproduction involves the growth of the embryo inside the maternal body. Here, however, the eggs also remain, which are literally incubated in the body and remain there until they hatch. Unlike what happens in viviparous, in this case there is no nutritional relationship between mother and growing embryo. Ovoviviparous they are the specimens of some species of fish, such as sharks, and then various reptiles, such as the viper, and some invertebrates.
L'platypus instead it is one of the very few oviparous mammals.
In general, taking into account that every single species has its own rules, among the oviparous here are the timing followed in the growth. And in reproduction. For oviparous fish and amphibians of the category of oviparous, the development of the embryo is fast, soon we find them adults and capable of self-sustaining and self-procuring food.
Being so fast, the eggs are small and with little reserve material. Always in the category oviperi, the growth of the embryo is much slower for reptiles and birds. The larval stage is often absent. This means that the egg must be larger and full of reserve substances for nourish the embryo.
In the viviparous we have said that the embryo stays in the mother's body and grows there drawing nourishment. For the marsupials, which are among the viviparous, the residence time in the female genitals is very short, the young are soon given birth because they have the opportunity to continue their development in the pouch, feeding from the breasts accessible to them.
It is different for i mammals with placenta, vivipers they too. In this case, the embryos complete the entire development process in the uterus, feeding on maternal blood that arrives thanks to placenta. Childbirth takes place, must take place, only once development has been completed.
Investigating the habits of the ovoviviparous vertebrates let's go back to reproduction through eggs which in this category are fertilized inside the mother's body. There remain the embryos and there they feed on egg reserves.
Unlike viviparous, the ovoviparous they do not derive nutrients directly from the mother who instead plays, with her own body, a protective role for the egg and the embryo itself. Having said that, if everything happens "inside", then we find ourselves with small generated already at the end of their development, therefore well formed and ready to live with no egg around.
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