Trypanosomes and trypanosomiasis / by A. Laveran and F. Mesnil. : Translated and much enlarged by David Nabarro.

  • Laveran, Alphonse, 1849-1922.
Date:
1907
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Licence: In copyright

Credit: Trypanosomes and trypanosomiasis / by A. Laveran and F. Mesnil. : Translated and much enlarged by David Nabarro. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    somes—that containing Trichomonas. We cannot agree with Kent, Danilewsky, and Doflein, who see in it a sufficient reason for placing Trypanosoma in a separate family, and we adopt the view of Senn, who regards Trypanosoma as a special genus of the family Oicomonadince or Ccrcouiuuadincs. Amongst all'the members of that family, trypanosomes included, movement takes place with the flagellum foremost. It is, therefore, natural to suppose that in all of them, including trypanosomes, the flagellated end is morphologically the anterior end. Recently, how- ever, it has been suggested by some that the morphologically anterior end of Trypanosoma is the non-flagellated one.^ That opinion is based on : (i) a consideration of Trichomonas,'^ in which the un- dulating membrane appears as a flagellum directed backwards, its free end being posterior (see Fig. 2, 5 /) ; (2) the fact that in Herpetomonas, as figured by Leger, the centrosome is close to the anterior extremity, and that it should be the same in Trypanosoma. Facts do not lend themselves to such an interpretation. The develop- ment of T. lewisi shows us, amongst other things, forms identical with the Herpetomonas of Leger, where the centrosome, at first situated in front of the nucleus, travels gradually towards the posterior end of the body, taking along with it the flagellum, which elongates and at the same time becomes separated laterally from the body of the parasite, so that it comes at last to be joined to it by merely a thin ridge—the undulating membrane. There is thus no evidence of a turning backwards of the flagellum ; and, as it is evident that the anterior extremity of the Herpetomonas-iovm is likewise the anterior extremity of the adult form, it must be agreed that it is always the flagellated end. [Leger,3 Liihe, and others regard trypanosomes as diphyletic in origin. Those with a morphologically anterior flagellum—recognisable by their becoming attached or fixed by the flagellated end—would be derived from a Herpetomonas or Crithidia, by the migration backwards of the centrosome and the gradual development of the undulating membrane; whereas those trypanosomes with a morphologically posterior flagellum — such parasites becoming fixed by their non-flagellated end—would be derived from a Trypanoplasma by the loss of its anterior flagellum. Mesnil* does not agree with this view, but regards all trypanosomes as having the flagellum morphologically anterior, and therefore considers the genus Trypanosoma monophyletic. In support of his view, he states that no importance can be attached to the pole of fixation, since in the same species one may find rosettes of trypanosomes with the flagella directed centripetally, and others with the flagella at the periphery. (See later under 7. leivisi.)] It remains now to review the genus Trypanoplasma. Senn places it in Bodonacce; Schaudinn, on the other hand, regards it as closely 1 Sambon, Journ. Trap. Med., v. 6, July i, 1903, p- 205, note ; J. Guiart, ibid., V. 7, January i, 1904, p. 4. [See also Liihe, Minchin, and Woodcock, in the articles previously quoted.] V 2 One can add, in the light of Li^ger's recent work, ' and of the Trypanoplasma: [L(^ger, C. K. Soc. Biol., v. 58, 1904, pp. 613-617.] ■• [Mesnil, Bull. hist. Past., v. 3, J905, p. 190.]