{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,3]],"date-time":"2026-04-03T15:54:43Z","timestamp":1775231683992,"version":"3.50.1"},"reference-count":56,"publisher":"Wiley","issue":"3","license":[{"start":{"date-parts":[[2005,5,3]],"date-time":"2005-05-03T00:00:00Z","timestamp":1115078400000},"content-version":"vor","delay-in-days":13332,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. Exp. Zool."],"published-print":{"date-parts":[[1968,11]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>The changes in fine structure of the growing female germ cell of <jats:italic>Arbacia lixula<\/jats:italic> and <jats:italic>Paracentrotus lividus<\/jats:italic> were examined by light and electron microscopy. During the previtellogenic growth stage of the oocyte, when the ribosome population in the cytoplasm increases several thousand times, the nucleolus also increases considerably in volume. A large number of ribosome\u2010like granules are concentrated in these nucleoli. Although particularly during this stage a passage of \u201cinformative\u201d material from the nucleus to the cytoplasm is to be expected, at present, evidence of any kind of extrusion has not been observed in these species. The only indirect morphological evidence for passage of material out of the nuclei might be the many newly formed pore complexes in the nuclear envelope. There is, however, strong evidence that they do not represent patent openings, since a dense, almost homogeneous, material is observed within the pore. Thus it is assumed that small molecules might pass through the pores freely, but not large particles the size of ribosomes.<\/jats:p><jats:p>Dense aggregates of two different types have been observed in secondary oogonia and in oocytes at the growth stage: one shows densely packed fibrils of about 80 \u00c5 and the other granules of 300 to 400 \u00c5.<\/jats:p><jats:p>At the end of vitellogenesis, the major nucleolus becomes vacuolated and disappears. At the same time several minor \u201cagranular\u201d nucleoli are formed. At meiosis these too disappear. In the mature egg few \u201cagranular\u201d nucleoli are seen. During cleavage the several \u201cagranular\u201d nucleoli are fibrillar, without ribosome\u2010like granules. From the blastula stage on, at a time when the cell divisions stop almost completely, the one or two nucleoli which can be observed in each nucleus have a small number of granules. During the following development the number of granules increases gradually up to gastrula, whereas the number of fibrils becomes more and more reduced.<\/jats:p>","DOI":"10.1002\/jez.1401690305","type":"journal-article","created":{"date-parts":[[2005,6,11]],"date-time":"2005-06-11T11:04:49Z","timestamp":1118487889000},"page":"293-313","source":"Crossref","is-referenced-by-count":36,"title":["Fine structure analysis of oogenesis in sea urchins"],"prefix":"10.1002","volume":"169","author":[{"given":"Giuseppe","family":"Millonig","sequence":"first","affiliation":[]},{"given":"Maria","family":"Bosco","sequence":"additional","affiliation":[]},{"given":"Liliana","family":"Giambertone","sequence":"additional","affiliation":[]}],"member":"311","published-online":{"date-parts":[[2005,5,3]]},"reference":[{"key":"e_1_2_1_2_1","doi-asserted-by":"publisher","DOI":"10.1083\/jcb.21.3.397"},{"key":"e_1_2_1_3_1","doi-asserted-by":"publisher","DOI":"10.1016\/0014-4827(55)90051-3"},{"key":"e_1_2_1_4_1","doi-asserted-by":"publisher","DOI":"10.1016\/0014-4827(56)90191-4"},{"key":"e_1_2_1_5_1","doi-asserted-by":"crossref","first-page":"660","DOI":"10.1007\/BF00338710","article-title":"Electron microscopy on the basophilic structures of the sea urchin egg","volume":"45","author":"Afzelius B. 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