Organoids

ORGANOIDS, ORGANELLES, is the name given, in contrast to the organs of multicellular animals, to the parts of the single cell of protozoan organisms (Protozoa) that serve them for the performance of various vital functions, e.g., cilia, digestive vacuoles, etc. Organoids that manage various aspects of one and the same physiological function form an organoid system (digestive organoid system, supporting organoid system, etc.). In the body of protozoa, at the present time, a whole series of organoid systems are distinguished: motor, digestive, supporting, contractile, excretory, and even nervous, although regarding the latter, there are still disagreements. Organoids that are part of various systems are analogized with the corresponding organs of multicellular animals and often bear the same names. For example, in the digestive system of ciliates, the opening serving for the intake of food is called the mouth, the opening intended for the excretion of waste is called the anus, or cytopyge, etc. Some authors, however, to emphasize the difference between the mouth of Protozoa and the mouth of multicellular animals, call the former the cell mouth (cytostom), the anus of protozoa the cell anus (cytopyge), etc. In other cases, many organoids of Protozoa were given somewhat different names from the very beginning than the corresponding organs of multicellular animals. Thus, in relation to the contractile fibers in the cell of protozoa, the term myonemes (in ciliates, gregarines, etc.) or myophrisks (in radiolarians) is applied; when Neresheimer (1908) found fibers in ciliates which he considered to be nervous, he gave them the special name neurophanes. The central nervous apparatus discovered by Sharp (1914), but disputed by European authors, which in significance corresponds to the cerebral ganglion of multicellular animals, received the name motorium. Sometimes organoids belonging to two different systems are in close organic connection with each other, as a result of which complex, dual-purpose organelle systems are obtained; in ciliates, their nervous center is connected by means of complex bundles of fibers (neurophanes) with all the motor organoids of the animal (cilia, myonemes). The entire aggregate of these cellular adaptations forms the so-called neuro-motor or neuro-kinetic apparatus. In some flagellates, there is the same union between the flagella (organoids of movement) and the axostyle (supporting rod)—a supporting-motor organoid system is obtained. Organoids reach the greatest diversity and complexity of structure in the class of ciliates, while the classes of sarcodines and SPOROZOA are the least rich in organoids.