Distribution of neoblasts and mitoses during the asexual reproduction of the planarian Dugesia tigrina (Girard).

The neoblast distribution in the prepharyngeal portion of the body remains unchanged during the asexual reproduction of planaria. During the first few days after fission, the number of neoblasts decreases in the portion of the body immediately adjoining the site of daughter zooid detachment and considerably increases in the regenerative bud. Starting with the fourth day after division, there is an increase in the number of neoblasts in the region of future fission, which can be regarded as one preparatory mechanism for the next fission. The mitosis distribution pattern is just the reverse: the regions of the body with the highest neoblast density are characterized by a low mitotic index or no dividing cells at all. The neoblast and mitosis distributions in the daughter zooid during its asexual reproduction cycle duplicate those observed in the maternal zooid.