Intermediate

Intermediate. Brain, see Diencephalon. Promitosis, a primitive form of indirect cell division (karyokinesis), described for a significant number of protozoa. According to the original meaning, under P., as proposed by Nasler, was understood a simplified mitosis, in which the cell centers (centrosomes) are enclosed within the nucleus (e.g. in some radiolarians Ceritropyxis and others). Subsequently, this term began to be interpreted more broadly in the above sense. One can distinguish several types of P. Thus, for a number of protozoa, a process has been described, in which the central mass of chromatin (karyosome) divides in two by constriction and moves to the poles, replacing the centrosphere, while the peripheral chromatin disintegrates into a certain number of parts, apparently corresponding to the chromosomes of normal mitosis. Finally, for the last type of P., which we encounter in a number of protozoa (e.g. amoebas), there are peculiar deviations in the number, external appearance, and behavior of the parts of the chromosomal apparatus.