Stages of development of a frog. Junior school - a living corner Who grows out of a tadpole
Whenever I pass in the spring by a pond, a ditch filled with water, or a sufficiently deep puddle and see gelatinous lumps of frog eggs laid there, I really like, as a child, to take quite a bit of this caviar, bring it home in a jar, place it into the aquarium, and then wait until tiny tadpoles appear from the caviar, when their hind and front legs begin to grow and when, finally, these tadpoles turn into small nimble frogs.
When the legs began to grow on the frogs, I made a small raft in the aquarium, where the frogs, which were about to appear from the tadpoles, could get out. And in my aquarium, an amazing transformation of an aquatic animal - a tadpole into an amphibious animal - a frog - took place. Over the course of one week, something happened at my place in our country for many, many years: the tadpole, before becoming a frog, as if repeating in its development the entire history of the transition of animals that had previously lived in water, on land.
If you watch all the tadpole transformations in the aquarium, you can notice a lot of interesting things. For example, at first the tadpole breathes with gills that are outside, - they are clearly visible on both sides of the head; then these external gills begin to disappear, and instead of them appear, as in fish, gill slits - now the tadpole breathes internal gills; and then gill slits overgrow - now the globastik is already beginning to breathe atmospheric air with the help of developed lungs.
On the twentieth - twenty-sixth day, the tadpoles begin to appear front and hind limbs. They appear at the same time, but the hind legs are more visible, and therefore, probably, believe that the tarsus first grows its hind legs.
But the most interesting changes begin to happen in about forty days - then the tin eel and finally turns into a frog. His small eyes become large, convex, a small mouth - large and wide. By this time, your aquarium must have a raft - a piece of artificial land where frogs could get out of the water; because now land also becomes their habitat.
The frogs that appeared were usually not kept at home; Gathering these kids carefully, I carried them to the place where I had recently found frog eggs and let them out in the grass near the water - by this time frogs appeared in the pond and in the ditch, and my pets quickly mastered. I did not let the frogs go at all because they bothered me. No, I like frogs and toads very much and often keep houses of different amphibians, but the trouble is that keeping frogs at home is difficult. They are very mobile, their jumps are great for a small terrarium - they hit the walls every now and then. In addition, frogs are also shy, and there is little pleasure in watching them in the terrarium. Another thing is the tadpoles emerging from caviar. Just remember that tadpoles, like all other animals living at home, need to be fed. In nature, they feed on algae, overgrown on the leaves of plants, pick up various organic residues. Therefore, when you keep the tadpoles at home, you must constantly bring from the pond either leaves of water lilies, then leaves of an arrow leaf, or even whole branches of small aquatic plants - from these leaves and branches of the tadpoles they will collect the necessary food.
You can give tadpoles and very little yeast (ordinary yeast on which the dough is placed) or feed them with dry nettles - a leaf of dry nettles must first be ground into powder.
Frogs, gametogenesis, fertilization and other seasonal events depend on numerous external factors. The life of almost all amphibians depends on the number of plants and insects in the pond, as well as the temperature of the air and water. There are various stages of development of frogs, including larval (egg - embryo - tadpole - frog). The metamorphosis of the tadpole into an adult is one of the most striking transformations in biology, since these changes prepare the aquatic organism for a terrestrial existence.
The development of frogs: photo
In tailless amphibians, such as frogs and toads, metamorphic changes are most pronounced, almost every organ undergoes modification. The shape of the body changes beyond recognition. After the appearance of the hind and forelimbs, the tail gradually disappears. The cartilaginous skull of the tadpole is replaced by the facial skull of a young frog. The horny teeth that the tadpole used to eat pond plants disappear, the mouth and jaws take on a new shape, the muscles of the tongue develop more strongly to make it easier to catch flies and other insects. The elongated colon, characteristic of herbivores, is shortened to adapt to the carnivorous diet of an adult. At a certain stage in the development of frogs, the gills disappear, and the lungs increase.
What happens immediately after fertilization?
Soon after, it begins to pass from one cell stage to another in the process of division. The first cleavage starts from the animal pole and extends vertically down to the vegetative pole, dividing the egg into two blastomeres. The second cleavage occurs at right angles to the first, dividing the egg into 4 blastomeres. The third furrow is located at right angles to the first two, being closer to the animal than to the vegetative pole. It separates the four upper small pigmented areas from the four lower ones. At this stage, the embryo already has 8 blastomeres.
Further splits become less regular. As a result, a unicellular egg gradually turns into a unicellular embryo, which at this stage is called a blastula, which even at the stage of 8-16 cells begins to acquire spatial cavities filled with liquid. After a series of changes, a single-layer blastula turns into a two-layer embryo (gastrula). This complex process is called gastrulation. The intermediate stages of frog development at this stage imply the formation of three protective layers: ectoderm, mesoderm, and endoderm, which are also known as primary. Later, larvae hatch from these three layers.
Tadpoles (larval stage)
The next after the embryo is the larva, which leaves the protective membrane 2 weeks after fertilization. After the so-called release, the frog larvae are called tadpoles, which are more like small fish about 5-7 mm long. The body of the larva includes a distinct head, trunk and tail. The role of the respiratory organs is played by two pairs of small external gills. A fully formed tadpole has organs adapted for swimming and breathing; the lungs of a future frog develop from the pharynx.
Unique metamorphoses
The water tadpole undergoes a series of changes, which eventually transform it into a frog. During metamorphosis, some larval structures are reduced, and some change. Metamorphoses initiated by thyroid function can be divided into three categories.
1. Changes in appearance. Hind limbs grow, joints develop, fingers appear. The forelimbs, still hidden by special protective folds, go outside. The tail is reduced, its structures break and gradually nothing remains in its place. Eyes from the sides go to the upper part of the head and become bulging, the system of the lateral line of organs disappears, the old skin is discarded, and new, with a large number of skin glands, develops. Horny jaws fall away with larval skin, they are replaced by true jaws, first cartilaginous, and then bone. Rupture of the mouth is greatly increased, allowing the frog to eat large insects.
2. Changes in internal anatomy. The gills begin to lose their meaning and disappear, the lungs become more and more functional. Corresponding changes occur in the vascular system. Now the gills gradually cease to play a role in the blood circulation, more blood begins to flow into the lungs. The heart becomes three-chambered. The transition from predominantly plant foods to a purely carnivorous diet affects the length of the digestive canal. It shrinks and twists. The mouth becomes wider, the jaw develops, the tongue enlarges, the stomach and liver also become larger. Pronephros is replaced by mesospheric kidneys.
3. Changes in lifestyle. During the transition from the larva to the adult stage of development of frogs, the amphibian lifestyle changes with the onset of metamorphosis. It often rises to the surface to swallow air and inflate the lungs.
Little Frog - A miniature version of an adult frog
At the age of 12 weeks, the tadpole has only a small tail residue and in appearance resembles a reduced version of an adult individual, which, by the 16th week, as a rule, completes the full growth cycle. The development and species of frogs are interconnected, some frogs that live at high altitudes or in cold places can live in the tadpole stage all winter. Certain species may have their own unique stages of development, which differ from traditional ones.
Frog life cycle
Most frogs breed in the rainy season when ponds are flooded with water. Tadpoles, whose nutrition is different from that of adults, can take advantage of the abundance of algae and vegetation in the water. The female lays eggs in a special protective jelly under water or on plants located nearby, and sometimes does not even care about offspring. Initially, embryos absorb their yolk reserves. As soon as the embryo has turned into a tadpole, the jelly dissolves and the tadpole leaves its protective shell. The development of frogs from eggs into an adult is accompanied by a number of complex changes (appearance of limbs, tail reduction, internal organ remodeling, and so on). As a result, an adult animal in its structure, lifestyle and habitat is significantly different from previous stages of development.
tailless amphibian.general description
At the initial stage, the tadpoles have a two-chamber heart, external gills (2-3 pairs), a long tail, a horny beak, lateral line organs, an adhesion organ, and one blood circulation.
After 3-4 months of development, metamorphosis occurs: another chamber appears in the heart, another circle of blood circulation appears, gills are reduced, and pulmonary respiration appears. Limbs grow and the tail disappears. The tail disappears due to autolysis, and the resulting substances and energy are used by other cells.
Tadpoles of different species vary significantly in size. So, for example, even within the same family of horned garlic ladies (lat. Megophryidae) at a late stage of development, the size of the tadpoles varies from 33 to 106 mm . The largest tadpoles are found in an amazing frog (lat. Pseudis paradoxa) - they reach a length of 25 centimeters, which is four times the length of an adult.
Research
In 2000, Richard Wassersug of the University of Dalhousie received the Shnobel Prize for reporting "On the comparative tastes of some of the tadpoles of Costa Rica in the dry season."
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References
Notes
Literature
- // Brockhaus and Efron Encyclopedic Dictionary: in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.
- G. R. Zug, L. J. Vitt, J. P. Caldwell. . - Academic Press, 2001. - ISBN 978-0-12-782622-6.
Excerpt from the Tadpole
“But what am I to do?”“Give it to me,” said Princess Marya. - I know…
Pierre looked into the eyes of Princess Marye.
“Well, well ...” he said.
“I know that she loves ... will love you,” Princess Marya recovered.
Before she could say these words, Pierre jumped up and grabbed Princess Mary by the hand with a startled face.
“Why are you thinking?” Do you think I can hope? You think?!
“Yes, I think,” said Princess Mary, smiling. - Write to parents. And instruct me. I will tell her when possible. I wish it. And my heart feels that it will be.
“No, that can't be!” How happy i am But it cannot be ... How happy I am! No, it can not be! - said Pierre, kissing the hands of Princess Marya.
- You go to Petersburg; it is better. And I'll write you, ”she said.
- To Petersburg? Go? Okay, yes, go. But can I come to you tomorrow?
The next day, Pierre came to say goodbye. Natasha was less lively than in earlier days; but that day, sometimes looking into her eyes, Pierre felt that he was disappearing, that neither he nor she was anymore, but there was one feeling of happiness. “Really? No, it cannot be, ”he said to himself with every look, gesture, word, filling his soul with joy.
When he, while saying goodbye to her, took her thin, thin hand, he unwittingly held her in his own for a little longer.
“Is this hand, this face, these eyes, all this alien to me treasure of female charm, is it really all will be forever mine, familiar, the same as I am for myself? No, It is Immpossible!.."
“Goodbye, Count,” she told him loudly. “I will be very waiting for you,” she added in a whisper.
And these simple words, the look and facial expression that accompanied them, for two months constituted the subject of inexhaustible memories, explanations and happy dreams of Pierre. “I will be very waiting for you ... Yes, yes, as she said? Yes, I will be very waiting for you. Ah, how happy I am! Well this is how happy I am! ” Pierre told himself.
In Pierre’s soul now nothing similar happened to what happened in her in the same circumstances during his matchmaking with Helene.
He did not repeat, as then, with painful shame, the words he had said, he did not say to himself: “Ah, why didn’t I say this, and why, why did I say“ je vous aime “then?” [I love you] Now, on the contrary, he repeated her every word, his own in his imagination with all the details of her face, smile, and did not want to diminish or add anything: he only wanted to repeat it. There was no doubt that what he had done was good or bad, and now there was no shadow. One terrible doubt sometimes crossed his mind. Is it all in a dream? Was Princess Marya wrong? Am I too proud and presumptuous? I believe; and suddenly, what should happen, Princess Mary will tell her, and she will smile and answer: “How strange! True, he was mistaken. Does he not know that he is a man, just a man, and I? .. I’m completely different, higher. "
What does a frog look like - everyone knows. And how is the birth of a frog? Is it true that different types of frogs reproduce and care for their offspring in different ways?
In this article we will talk about how nature arranged the process of the birth of the most. Typically, these amphibians are born in a pond or lake. The female frog leaves eggs only in stagnant water. After a certain period of time, tadpoles appear from the laid eggs, then they turn into small frogs ... so we used to think when looking at the frogs that live in our country, but in reality ...
In fact, not all species of frogs reproduce equally. The main "innovators" in the reproductive sphere are those frogs that live in the tropics. Firstly, the number of species of tailless amphibians that we are talking about in the tropical zones exceeds all conceivable ideas. A large number of predators, every now and then wanting to eat frog eggs, makes these amphibians invent various ways to save future offspring.
The birth of glass frogs
Females produce eggs that look like gelatinous mass. This "mass" is attached to the back of the sheet (it is important that the sheet is located directly above the water). The father of the family becomes a guard for future offspring. When the tadpoles emerge from the eggs, they slide off the leaf directly into the pond and there is already a further transformation into an adult.
The birth of a South African frog
Have you heard of the “foam houses”? This is not just an unusual substance, but a real shelter in which South African frogs hide their eggs. How is foam formed? In order to create such a "house", the female frog secretes a special substance, and the hardworking male whips it into foam. The top layer of the foam house hardens, and the eggs can comfortably continue to develop inside without fear of being eaten.
The birth of poisonous poison frogs
Poisonous South American frogs also give their offspring life in an unusual way. They, like their other relatives, lay eggs (placing it on moist soil). Then they carefully and very zealously guard the eggs. Well, when the tadpoles emerge from the eggs, they immediately climb onto the back to their parent. What for? To move from earth to tree. Having found the leaves of the bromeliad plant (which winds around the trees), the mother frog places the tadpoles in the funnel located at the base of the bromeliad leaf (where water always accumulates after rains). Here the tadpoles find temporary shelter until their parent finds a nearby body of water and transfers them into it for subsequent maturation.
The birth of dwarf marsupial tree frog
Yes, yes, you didn’t hear exactly “marsupial”. By the way, the birth of cubs in this frog is similar to the method of reproduction in a kangaroo. The frog has a special leather pocket, where the laid eggs are placed. Unlike a kangaroo, a tree frog pocket is located on the back. So a caring mother carries her future babies until the time comes for them to become tadpoles. Then tree frog carries future frogs to the reservoir and releases them.
The birth of a rain frog
The unusual arrangement of the eggs of these frogs allows you to be born not as a tadpole, but immediately as a small adult. The fact is that the internal composition of the egg is such that it has a sufficient supply of nutrients so that the tadpole feeds and survives until it turns into a frog without leaving the egg shell.
