Dugesia refers to the planarian flatworm. While this primitive life form has a nervous system, it is different from the central nervous system found in other invertebrates and worms. As a matter of fact, dugesia's central nervous system is used a lot in regeneration research as well as developmental biology.
If you check the central nervous system of the dugesia, you will see that its nervous system though simple has many features that are also seen in vertebrates. For instance, planarians have a primitive brain, multi-polar neurons as well as dendritic spines. The sensory organs are present in the anterior part of the primitive brain. A dugesia's head is shaped like a triangle and consists of 2 eyespots and lateral horns, giving the worms a bilateral symmetry.
The reason that scientists are interested in the evolution of dugesia central nervous system is the similarity with the vertebrate nervous system where physiology and cell morphology is concerned. It has also been noted that practically all neurotransmitters present in mammals are also present in dugesias. This makes the dugesia extremely useful when studying the development of the nervous system and the regeneration of the nervous system.
The dugesia central nervous system looks like a ladder, with 2 nerve cords and a primitive brain (ganglia) present at the anterior region. The 2 nerve cords are connected to one another with transverse nerves and this ensures that the 2 sides are synchronized with one another. The sensory receptors of the dugesia are situated in the auricles, and the eyespots on the anterior region have photoreceptors.
Out of all the primitive invertebrates, the dugesia has the most developed central nervous system. In order to understand the evolution of dugesia central nervous system, researchers separated a neural marker gene from the Dugesia japonica. They then checked the central nervous system structure of the dugesia using in situ hybridization process. The researchers found the central nervous system of the dugesia is situated along the anterior posterior axis, which has a distribution similar to the primary neurons found in vertebrate embryos. These primary neurons in the embryos then go on to form the nervous system during the neural plate stage. However, the central nervous system of vertebrates is present on the dorsal side. Based on the data collected, researchers came to the conclusion that the development of the dugesia's central nervous system along the anterior posterior axis must have taken place during the early stages of evolution long before the nervous system's location went from ventral to the dorsal part of the body.
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