For example, a planarian split lengthwise or crosswise will fundamentals of anatomy and physiology pdf free into two separate individuals. Some also may move by undulations of the whole body by the contractions of muscles built into the body membrane. Triclads play an important role in watercourse ecosystems and are often very important as bio-indicators.
The planarian has very simple organ systems. The mouth is located in the center of the underside of the body. Digestive enzymes are secreted from the mouth to begin external digestion. The pharynx connects the mouth to the gastrovascular cavity. This structure branches throughout the body allowing nutrients from food to reach all extremities. Planaria eat living or dead small animals that they suck up with their muscular mouths. Food passes from the mouth through the pharynx into the intestines where it is digested by the cells lining the intestines.
Planaria receive oxygen and release carbon dioxide by diffusion. Also, flame cells remove unwanted liquids from the body by passing them through ducts which lead to excretory pores, where waste is released on the dorsal surface of the planarian. There are many transverse nerves connected to the nerve cords extending from the brain, which makes the nerve system look like a ladder. With a ladder-like nerve system, it is able to respond in a coordinated manner. The planarian has a soft, flat, wedge-shaped body that may be black, brown, blue, gray, or white. Unsourced material may be challenged and removed. There are sexual and asexual planaria.
Thus, one of their gametes will combine with the gamete of another planarian. Eggs develop inside the body and are shed in capsules. Weeks later, the eggs hatch and grow into adults. Some species of planaria are exclusively asexual, whereas some can reproduce both sexually and asexually.
Planaria can be cut into pieces, and each piece can regenerate into a complete organism. It’s this feature that gave them the famous designation of being “immortal under the edge of a knife. 277th of the organism it is cut from, can regenerate back into a complete organism over the course of a few weeks. They are the only proliferating cells in the worm, and they differentiate into progeny that replace older cells. The organism itself does not have to be completely cut into separate pieces for the regeneration phenomenon to be witnessed. In fact, if the head of a planaria is cut in half down its center, and each side retained on the organism, it is possible for the planaria to regenerate two heads and continue to live. They discovered that one of the amputated fragments sent to space regenerated into a double-headed worm.
After repeating this several times they took away the electric shock, and only exposed them to the bright light. The flatworms would react to the bright light as if they had been shocked. He reported that the flatworms learned to associate the bright light with a shock much faster than flatworms who had not been fed trained worms. This experiment intended to show that memory could be transferred chemically. The experiment was repeated with mice, fish, and rats, but it always failed to produce the same results. The perceived explanation was that rather than memory being transferred to the other animals, it was the hormones in the ingested ground animals that changed the behavior. Subsequent explanations of maze-running enhancements associated with cannibalism of trained planarian worms were that the untrained flatworms were only following tracks left on the dirty glassware rather than absorbing the memory of their fodder.
In 2012, Tal Shomrat and Michael Levin have shown that planarians exhibit evidence of long-term memory retrieval after regenerating a new head. Schmidtea mediterranea: A Model System for Analysis of Motile Cilia”. NOT YOUR FATHER’S PLANARIAN: A CLASSIC MODEL ENTERS THE ERA OF FUNCTIONAL GENOMICS”. When does a ganglion become a brain? Evolutionary origin or the central nervous system”. Recording and spectrum analysis of the planarian electroencephalogram”.