The genetics of Paramecium aurelia / [Geoffrey Beale].

  • Beale, Geoffrey, 1913-
Date:
1954
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: The genetics of Paramecium aurelia / [Geoffrey Beale]. Source: Wellcome Collection.

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    The Genetics о/Paramecium aurelia unknown. By certain serological tests, as described in Chapter 4, no differences corresponding to the mating type differences have been detected. After the animals have been paired for some time, the mouths become closed, and eventually the gullets are reduced to rudi¬ ments. Consequently the animals do not feed during conjuga¬ tion, and partly for this reason, become much reduced in size. Meanwhile, the interior contents undergo a radical reorganiza¬ tion. According to Hertwig (1889) new mouths and gullets are formed in each conjugating animal by budding from rudiments of old ones, as during binary fission, but with the difference that, at conjugation, the old mouth and gullet is eventually lost altogether. The contractile vacuoles, however, continue to func¬ tion normally throughout conjugation (Wichterman, 1953). The whole process of conjugation normally lasts, at 27-29° C., for 51 or 6 hours, and at lower temperatures considerably longer. Exceptionally, however, the animals may remain attached for longer periods at the 'paroral cone' region, but not at the anterior 'hold-fast' region. Indeed, sometimes the cytoplasmic connexion between the animals at the 'paroral cone' region never breaks, and permanent double animals are formed, as described by Sonneborn (1942^). The nuclear changes which take place during conjugation, and after, are not entirely clear from cytological observation, and it is necessary to make use of combined cytological and genetic data in order to complete the picture. In addition, in¬ ferences may be drawn from known cytological processes in con¬ jugation of other ciliates, since the basic stages seem to be similar in many other genera (see Dogiel, 1951 ). Most of our knowledge of the cytology of conjugation in P. aurelia is based on two re¬ markable papers which appeared as far back as 1889, by Maupas and Hertwig respectively, working independently. Diller (1936) and Sonneborn (1954^) have added some further details. The most striking nuclear change during conjugation is the disintegration of the macronucleus. During the second half of the period during which the animals are paired, this structure stretches out into a long skein, which then breaks into more or less rounded fragments, the number of which may be as many as fifty-seven, according to Maupas. The fragments are 24
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