| Author Title Journal |
Lepori NG (1949) Richerche sulla ovogenesi e sulla fecondazione nella planaria Polycelis nigra Ehrenberg con particolare rigardo all'ufficio del nucleo spermatoco. Caryologia (Pisa) 1:280-295 |
Abstract / Notes
In oocytes of Polycelis nigra from different places in Italy, 24 bivalent chromosomes were counted. Oocytes leaving the ovary exhibit 24 metaphase tetrads. Polar bodies are only formed after a sperm derived from another animal has penetrated the oocyte. Though Polycelis nigra is a hermaphrodite, such fecundation is indispensable for the development of the egg. During the cleavage of the egg, the haploid chromosome number, 24, was always noted. The sperm nucleus thus plays a mere activating part. As in a few other cases, such as the nematode Rhabditis , there is a gynogenetic mode of development of eggs. This explains maternal inheritance such as was observed by Benazzi in his genetical investigations of Polycelis. The method whereby the 2n number of chromosomes is re-established has still to be cleared ap
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