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  • 1
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The problem of the sexual differentiation of the neoblasts of planarians is approached on the basis of karyological evidence assembled by the author and by his collaborators. In the polyploid and pseudogamic biotypes of Dugesia benazzii, D. lugubris and Polycelis nigra, the transformation of the neoblasts into oogonia or spermatogonia is accompanied by variations in the chromosome set. These variations may be considered to be dependent upon the gradient of sexuality — that is, of the territorial influences that determine the evolution in a female or a male direction. Significant evidence is also inferred from the chromosome cycle of hybrids between amphigonic diploid biotypes and polyploid biotypes. A new direction of research, based on the comparison between anterior and posterior regenerated segments of experimental polyploids with variable chromosome sets aims at establishing possible regional differences in the set of the neoblasts.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 3 (1950), S. 474-482 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung Bei der Rasse G von Dugesia benazzii von Sardinien hat das Spermatozoon nur die Funktion der Entwicklungserregung, da die Amphimixis nicht erfolgt und der männliche Vorkern wie ein Eichtungskörper eliminiert wird. Das Ei entwickelt sich allein mit der weiblichen Chromosomengarnitur (Gynogenese), und das erklärt die vom Autor an dieser Planarie festgestellte mütterliche Vererbung. Auch bei den italienischen Rassen von Polycelis rigra erfolgt die Entwicklung durch Gynogenese nach den genetischen Untersuchungen des Autors und den cytologischen von N. G. Lepori.
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  • 3
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Biotype E of Dugesia lugubris has a haploid complement of 4, comprising 3 acrocentrics of different length and a short chromosome; biotype F has a haploid complement of 3, with a long metacentric, an acrocentric and a short chromosome. A karyometrical analysis has shown that the metacentric chromosome of biotype F derived from a centric fusion between the acrocentrics 1 and 3 of biotype E. — The evolutionary meaning of this centric fusion is discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 84 (1981), S. 163-165 
    ISSN: 1573-5117
    Keywords: Turbellaria ; Dugesia ; karyology ; reproduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Dugesia sanchezi reproduces in nature both sexually and by fission. Laboratory cultures have shown that fissioning is controlled by genetic factors. From sexual specimens randomly mated, 105 sexual and five fissiparous offspring were obtained. The former produced almost exclusively sexual descendents while the latter gave rise to fissiparous individuals, although successively many of them became sexual. These ex-fissiparous specimens show a high fertility and their offspring were almost all fissiparous, with the same characteristics displayed by the preceeding fissiparous generation. Some hypotheses are advanced in order to attempt a genetical interpretation of these results.
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  • 5
    ISSN: 1573-5117
    Keywords: Turbellaria ; Dugesia ; reproduction ; karyology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract One of the biotypes of the planarian Dugesia benazzii is triploid in the somatic line, hexaploid in the female line owing to a chromosome set doubling, and diploid in the male line due to a haploid set elimination. In a population of this biotype only 50% of the oocytes are hexaploid, the others being triploid as a results of the lack of set doubling; the male line is always diploid. After a long period of laboratory culture most of the individuals became asexual and fissiparous. Almost all the oocytes of the few specimens which have remained sexual showed triploid complement; B-chromosomes also appeared. These events represent the manifestation of a new genetic background which act upon the two germ lines in different ways and moments. These topics are discussed.
    Type of Medium: Electronic Resource
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