In this article we will look at the stages of frog development. But first, let's talk a little about what these creatures are. The frog belongs to the class of amphibians, the tailless order.
Many have noticed that her neck is not expressed - it seems to have grown together with the body. Most amphibians have a tail, which the frog does not have, which, by the way, is reflected in the name of the detachment.
The development of a frog goes through several stages, we will return to them immediately after we analyze some of the features of these creatures.
What a frog looks like
For starters, the head. Everyone knows that the frog has rather large and expressive eyes located on both sides of its flat skull. Frogs also have eyelids; this feature is inherent in all terrestrial vertebrates. The mouth of this creature has small teeth, and a little above it are two nostrils with small valves.
The front limbs of frogs are less developed than the hind limbs. The first have four fingers, the second - five. The space between the fingers is webbed, and there are no claws.
The development of the frog is taking place inmultiple stages:
- Spawn throwing.
- Early stage tadpoles.
- Later stage tadpoles.
- Adults.
Their fertilization is external - the males fertilize the eggs already laid by the female. By the way, there are species that lay more than 20 thousand eggs in one throw. If everything goes well, then ten days later tadpoles are born. And after another 4 months, full-fledged frogs are obtained from them. Three years later, a mature individual grows up, which is completely ready for reproduction.
Now a little more about each step.
Caviar
Now we will analyze all the stages of frog development separately. Let's start with the very first - eggs. Although these creatures live on land, during spawning, they go into the water. This usually happens in the spring. Masonry takes place in quiet places, at a shallow depth, so that the sun can warm it up. All eggs are interconnected, and this mass resembles jelly. One teaspoon is barely enough from one individual. All this jelly mass is necessarily attached to the algae in the pond. Small species lay about 2-3 thousand eggs, large individuals - 6-8 thousand.
The egg looks like a small ball, about 1.5 millimeters in diameter. It is very light, has a black shell and increases in size over time. Gradually, the eggs move on to the next stage of frog development - the appearance of tadpoles.
Tadpoles
After birthtadpoles begin to feed on the yolk, which still remains in small quantities in their intestines. This is a very fragile and helpless creature. This individual has:
- poorly developed gills;
- mouth;
- tail.
Tadpoles, in addition, are equipped with small Velcro, with which they are attached to various water objects. These Velcro are located between the mouth and abdomen. In the attached state, the babies are about 10 days old, after which they begin to swim and eat algae. Their gills gradually grow over after 30 days of life and, as a result, are completely covered with skin and disappear.
It is also important to know that even tadpoles already have the small teeth needed to eat algae, and their spiral-shaped intestines allow them to extract the maximum nutrients from what they eat. In addition, they have a chord, a two-chambered heart and blood circulation in the form of a single circle.
Even at this stage of frog development, tadpoles can be considered quite social creatures. Many of them interact like fish.
The appearance of legs
Since we are considering the development of a frog in stages, the next step is to select tadpoles with legs. Their hind limbs appear much earlier than the front ones, after about 8 weeks of development - they are still very tiny. In the same period, you can notice that the head of the kids becomes more distinct. They can now eat larger prey, such as the deadinsects.
The forelimbs are just beginning to form, and here one can single out such a feature - the elbow appears first. Only after 9-10 weeks will a full-fledged frog form, however, much smaller than its mature relatives, and even having a long tail. After 12 weeks, it completely disappears. Now the little frogs can go on land. And after 3 years, a mature individual will form and will be able to continue its genus. We will talk about this in the next section.
Adult
After three long years have passed, the frog can reproduce into the world. This cycle in nature is endless.
To consolidate, let's list the stages of development of the frog again, the scheme will be our assistant in this:
fertilized egg represented by an egg - tadpole with external gills - tadpole with internal gills and skin respiration - formed tadpole with lungs, limbs and gradually disappearing tail - frog - adult.
