Piotr Świątek

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The genus Taraxacum Wigg. (Asteraceae) forms a polyploid complex within which there are strong links between the ploidy level and the mode of reproduction. Diploids are obligate sexual, whereas polyploids are usually apomictic. The paper reports on a comparative study of the ovary and especially the ovule anatomy in the diploid dandelion T. linearisquameum(More)
Glossiphonia heteroclita has paired ovaries whose shape and dimensions change as oogenesis proceeds: during early previtellogenesis they are small and club-shaped, whereas during vitellogenesis they broaden and elongate considerably. During early oogenesis (previtellogenesis), each ovary is composed of an outer envelope (ovisac) that surrounds the ovary(More)
Piscicola has a pair of elongated sac-shaped ovaries. Inside the ovaries are numerous small somatic cells and regularly spherical egg follicles. Each follicle is composed of three types of cells: many (average 30) germ cells (cystocytes) interconnected by intercellular bridges in clones (cysts), one intermediate cell, and three to five outer follicle cells(More)
Stereological analysis of the ultrastructure of primordial germ cells (PGCs) and the somatic (ectoderm) cells in two developmental stages of embryos and freshly hatched juveniles of Allacma fusca have shown great differences in mitochondria volume density (vd) between the two types of cells. In younger embryos (migration phase of the PGCs) the vd of(More)
The organization of the ovaries in representative of the Salifidae (Hirudinida, Erpobdelliformes) was studied at the ultrastructural level for the first time. Like in other leeches, the ovaries of Barbronia weberi are composed of an outer envelope (i.e., an ovisac made up of two coelomic epithelia, muscle cells, and connective tissue) and several internal(More)
In Hirudo medicinalis and Haemopis sanguisuga, two convoluted ovary cords are found within each ovary. Each ovary cord is a polarized structure composed of germ cells (oogonia, developing oocytes, nurse cells) and somatic cells (apical cell, follicular cells). One end of the ovary cord is club-shaped and comprises one huge apical cell, numerous oogonia, and(More)
Oogenesis in the glossiphoniid leech Glossiphonia heteroclita (Hirudinea, Rhynchobdellida) is nutrimental, i.e., the growing oocyte is supported by specialized germline cells, the nurse cells. The main function of the nurse cells is to provide oocytes with cell organelles and RNAs (mainly rRNA). However, in studied leech species, irrespective of the(More)
Animal germ cells tend to form clonal groups known as clusters or cysts. Germ cells within the cyst (cystocytes) are interconnected by intercellular bridges and thus constitute a syncytium. Our knowledge of the mechanisms that control the formation of germ-cell clusters comes from extensive studies carried on model organisms (Drosophila, Xenopus). Germ-cell(More)
This paper presents information on the organization of the midgut and its epithelium ultrastructure in juvenile and adult specimens of Piscicola geometra (Annelida, Hirudinea), a species which is a widespread ectoparasite found on the body and gills and in the mouth of many types of fish. The analysis of juvenile nonfeeding specimens helped in the(More)
Beginning with light microscopy studies in the late 19th century, the placental “nutritive tissue” in carnivorous plants of Utricularia spp. has been well described by several authors. Based on observations of direct contact between the embryo sac and the “nutritive tissue” and the lack of vascularization of the ovule, it has been suggested that this(More)