Volume 1

Essays upon heredity and kindred biological problems / by August Weismann ; edited by Edward B. Poulton, Selmar Schönland, and Arthur E. Shipley, authorized translation.

  • Shipley A. E. (Arthur Everett), Sir, 1861-1927.
Date:
1891-1892
Catalogue details

Licence: Public Domain Mark

Credit: Essays upon heredity and kindred biological problems / by August Weismann ; edited by Edward B. Poulton, Selmar Schönland, and Arthur E. Shipley, authorized translation. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    I.] reproduce sexually, may remain alive for more than a week waiting for a male: after fertilization, however, they lay their eggs and die, while the parthenogenetic females of the same species lay their eggs and die immediately after leaving the cocoon ; so that while the former live for many days, the latter do not last for more than twenty-four hours. ' The partheno- genetic form of Solenobia triquetrella, soon after emergence, fays all her eggs together in the empty case, becomes much shrunken, and dies in a few hours.' (Letter from Dr. Speyer, Rhoden.) Note 10. Intermingling during the Fission of Unicellular Organisms Fission is quite symmetrical in Amoebae, so that it is impos- sible to recognise mother and daughter in the two resulting organisms. But in Euglypha and allied forms the existence of a shell introduces a distinguishing mark by which it is possible to discriminate between the products of fission; so that the offspring can be differentiated from the parent. The parent organism, before division, builds the parts of the shell for the daughter form. These parts are arranged on the surface of that part of the protoplasm, external to the old shell, which will be subsequently separated as the daughter-cell. On this part the spicules are arranged and unite to form the new shell. The division of the nucleus takes place after that of the proto- plasm, so that the daughter-cell is for some time without a nucleus. Although we can in this species recognise the daughter-cell for some time after separation from the parent by the greater transparency of its younger shell, it is never- theless impossible to admit that the characteristics of the two animals are in any way different, for just before the separation of the two individuals a circulation of the protoplasm through both shells takes place after the manner described in the text, and there is therefore a complete interminghng of the substance of the two bodies. The difference between the products is even greater after transverse fission of the Infusoria, for a new anus must be ' Cf. August Gruber, ' Der Theilungsvorgang bei Euglypha alveolata,' and 'Die Theilung der monothalamen Rhizopoden,' Z. f. W. Z., Bd. XXXV. and XXXVI., p. 104, 1881. F