May 20 - Day of the donor
Reproduction of new bodies to replace the lost
(regeneration) — a phenomenon that is widespread in the animal Kingdom, especially in his lower representatives. In unicellular animals (protozoa, Protozoa) reproduction of new bodies is closely related to the process of reproduction.
Ciliates in most cases multiply by transverse division; thus, for example, the crown of cilia present on the anterior end of the body, for the back half of the infusoria, which must be separated and give rise to a new individual, is formed again on her front end, even before the separation of the two halves; here the reproduction of a new body precedes the division.
Was made the experience above the artificial division of infusoria; if large, elongated in the length of the ciliate stentor, with clearly-seen by the kernel, and atrial rim on the front end, cut crosswise, then each piece will turn into a whole new animal, if only there was a segment of the nucleus. Separated from the ciliate part of the protoplasm without nucleus can't recover to a new animal and die. Between multicellular animals (Metazoa) the ability to create new organs to replace the lost is found in the varying degrees.
The new body is formed in a similar manner, how is it formed in the embryo; the cells adjacent to the place where resided the authority would lose their special nature, which was inherent in the power of histological differentiation, begin to vigorously grow and provide material for the development of a new body; in this case epithelial cells give rise only to the epithelium, etc.
The cells do not extend beyond the functions of the embryonic leaf, from which they came. The less differentiated the organism, the greater its ability to reproduce; similarly in the embryo and even the young animal's ability is more than that of an adult. An example of a very broad ability play can serve as a freshwater Hydra (Hydra, an animal from the type of the coelenterates).
The experiments on it were made even in the last century Trambeam and filed at the time of the greatest interest. If the body of a Hydra is cut into pieces in the longitudinal or in the transverse direction, even small segments can give rise to new individuals; the mouth and tentacles are always formed at the front end of each segment.
The latter phenomenon can be considered a General rule for all cases, recovery in the animal Kingdom: in place of the lost body always a new same. However, not so long ago, Loeb was able to show that some animals, namely hydropolyp, and the possible return of the phenomenon. If you cut a piece of stem of the Tubularia (hydroid of the suborder Gymnoblastea) and stick this cut in the sand the end that was originally facing the head (the hydrant), the new hydrant is formed on the opposite end, where, as a matter of fact, he had formed a root.
If we attach the segment so that both ends protruded freely in the water, the new hydrants are formed on both ends: on oral and aboral. This phenomenon — the formation in place of the lost authority of the same, but another authority, Loeb gave the name of heteromorphosis.
Between the worms, the organisms are incomparably more perfect than hydropolyp, the ability to reproduce new bodies still in some cases still extremely high. If you cut it in half, the earthworm (Lumbricus), then cut off the rear half of a new head end, with nerve nodes, esophagus, etc. similarly, the front half is formed the rear end of the body; the original two new animal are formed. This ability to have many ciliary and annelid worms (Turbellaria, and Annelides).Wide ability have play echinoderms, especially sea stars. In case of loss of one or more rays in their place grow new ones; but, in addition, the separated beams have the ability to re-produce the Central disc of the body and new rays.
In these cases (Hydra, worm, starfish) reproduction of new bodies borders on asexual reproduction; many stars have the ability to spontaneously divide into two or more parts, which are then transformed into new animals; some rays alternately are separated from the circle at the base and each of them plays then a new circle with the other hand.
How big is the role of this process in the reproduction, evident from the fact that in some species, such as Ophidiaster Ehrenbergii, in the Red sea, rare instances with correctly developed, the same size hands. From this capacity lower Metazoa during the mechanical separation of the body develop from both parts of a new animal was supposed to happen the ability of asexual reproduction by dividing, with the necessary bodies are developing again to the separation of both species; this division can reproduce many coelenterates Turbellaria and Annelides.In animals of the higher types the ability to play a more limited and never leads to reproduction.
Between arthropods (Arthropoda) and soft (Mollusca) the ability of this very small; crayfish grow back severed limbs, especially the claws; a land snail grows to cut off a tentacle with the eye end, with the last developing only in case when the operation has not been damaged the so-called mapalaway ganglion (F u hlerganglion). Some of the sea squirts (Ciona intestinalis) retrieves all of the Central nervous system consisting of a single ganglion, situated at the top of the body, between the two siphons;if it cut out, after some time formed a new one. The sensitivity and reflex sokratitelnoj animal do not disappear, but only fall.
In vertebrates the ability to reproduce new bodies exists only in the lower classes, amphibians and reptiles; Triton grow severed limbs and tail; lizard-retrieves easy snap-off tail; vosstanavlivayutsya not only bones and muscles but also the back part of the spinal cord. But the traces of this ability exist in higher vertebrates; in humans has also been seen that in case of loss of the last joint of a finger sometimes on the penultimate joint has evolved a rudiment of the nail.
In greater extent in warm-blooded recovery of individual tissues: blood (and blood vessels), epithelium and its derivatives, and nervous tissues. Especially curious bone repair. If the articular end of the bone cut, it can again be restored, albeit in an abbreviated form; again healed a chipped or sawed pieces of bone.
The ability of re-producing the bone tissue of the hymen belongs to the periosteal (periosteum) and bone marrow. A stand-alone piece of periosteum, being moved even to a completely different area of the body, produces a proportionately large piece of bone; in surgical operations carefully try to preserve the periosteum, as hopes for a recovery from him in remote parts of the bone. This ability persists even when the hymen periosteal transfer from another species (periosteal membrane forms a puppy bone in the body of a rabbit).
See. Carri ere, "Studien u ber die Regenerationserscheinungen bei den Wirbellosen. I. Die Regeneration bei den Palmonaten" (Wurzburg, 1880);
Fraisse, "Die Regeneration von Geweben und Organen bei den Wirbelthieren" (Cassel and Berlin, 1885);
Loeb, "Untersuchungen zur physiologischen Morphologie der Thiere" (I-II, Wurzburg, 1891—92).
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