'Das Keimplasma': the continuity of the germ plasm and the mouse-tail experiment

1885–1892 Life and health theory

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A doctrine that divides the organism into two non-communicating parts: the germ plasm, which passes from generation to generation and lies in the nucleus, and the soma, the body built from it that dies. It follows that what the body acquires is not inherited.

The doctrine is set out in 'Das Keimplasma' (1892) by the German August Weismann. To test the non-transmission of acquired characters he cut off the tails of mice for five successive generations and obtained 901 young with normal tails. On purely theoretical grounds he inferred that a reduction division must occur in the maturation of the germ cells, halving the number of 'nuclear loops', and cytologists confirmed it.

The model of the hereditary substance as a hierarchy of nested units did not survive Mendelism and the chromosome theory, but the distinction between germ line and soma remained.

Why this date

The date follows 1892, the year of the book 'Das Keimplasma. Eine Theorie der Vererbung' (Jena: Fischer; English translation 'The Germ-plasm', London, 1893). The lower bound of the label is the essay 'Die Continuität des Keimplasmas' of 1885, in which, according to Robinson's DSB article, Weismann first placed the germ plasm within the nucleus. The tail-amputation experiment on mice was reported at the meeting of German naturalists at Cologne in September 1888; in the English 'Essays upon Heredity' (Oxford, 1889) Weismann gives the tally: 901 young from five generations of mutilated parents without a single shortened tail.

What it grew from

• Chromatin and mitosis: longitudinal splitting of the nuclear threads in cell division

  influenced · Confidence: medium

  Weismann built his germ plasm theory with the cytology of nuclear division before him: the longitudinal splitting of the threads shown by Flemming gave him the image of equal and unequal division of the hereditary substance, from which he inferred the reduction division.

  Dispute: Robinson notes that Weismann was influenced most strongly not by Flemming himself but by Wilhelm Roux's interpretation of mitosis, and that Weismann used the 'threads' as ready cytological material for a speculative scheme. The link is therefore drawn as influence and not as a prerequisite.

  Link sources

  • Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 20 Sep 2026

    Since he did not subscribe to the structure Naegeli claimed for the idioplasm, Weismann continued to develop his own concept, but kept in mind the cytological researches then under way.

  • Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 20 Sep 2026

    In 1875 Oscar Hertwig had seen the appartent fusion of the nuclei during fertilization; and in 1879 Walther Flemming had clearly shown that the threads seen in the nucleus split longitudinally, and had pointed to the possible significance of this segmentation.

  • Frederick B. Churchill, Weismann, August Friedrich Leopold, New Dictionary of Scientific Biography (2008) Verified 20 Sep 2026

    When Weismann introduced the term amphimixis in 1891, he was building on two decades of research in nuclear cytology

  • William Bechtel, Andrew Bollhagen, Philosophy of Cell Biology, The Stanford Encyclopedia of Philosophy (2021) Verified 20 Sep 2026

    Soon after researchers such as Weismann and Correns pointed to links between chromosome transmission and heredity, but it was Boveri (1902) and Sutton (1903) who provided the compelling evidence that Mendel’s factors (what would soon be called genes) are in or on chromosomes.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

What grew out of it

• Johannsen: pure lines, genotype and phenotype

  influenced · Confidence: medium

  Johannsen's genotype grew out of a polemic with Weismann's germ plasm: the new terms were introduced to get rid of a 'purely speculative morphological' view of heredity, while the idea itself of a hereditary constitution independent of the body was already present in Weismann and Galton.

  Dispute: The influence here is negative, by repulsion: Johannsen admitted the likeness of the genotype to the 'Keimplasma' but held Weismann up as an example of how not to theorise.

  Link sources

  • Robert C. Olby, Mendel, Mendelism and Genetics, MendelWeb (1997) Verified 20 Sep 2026

    The hallmark of Johannsen's contribution was the introduction of new terms with the deliberate aim of banishing what he regarded as the many erroneous associations which old terms carried. Thus the term germplasm had a Weismannian context, and that was a 'purely speculative morphological view of heredity without any suggestive value.'

  • Nils Roll-Hansen, The holist tradition in twentieth century genetics, Journal of Physiology 592 (11), 2431-2438 (2014) Verified 20 Sep 2026

    What an offspring receives from its parents is the genotype inherent in their gametes. Moreover, each generation produces gametes independently of its personal qualities. This reminds of Galton's 'stirp' and Weismann's 'Keimplasma', but according to Johannsen they had not freed their thinking from morphological preformation.

  • Nils Roll-Hansen, The holist tradition in twentieth century genetics, Journal of Physiology 592 (11), 2431-2438 (2014) Verified 20 Sep 2026

    One reason for this negative attitude to chromosome theorizing was his deep scepticism concerning Weismann's speculations about embryological development.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Boveri's multipolar mitoses: chromosomes are qualitatively different and individual

  influenced · Confidence: medium

  Weismann placed the hereditary substance in the nucleus while holding all chromosomes to be equivalent; Boveri's double-fertilization experiment bore precisely against that assumption and showed that chromosomes differ in quality.

  Dispute: The link is double: one and the same doctrine gave Boveri his premise (the hereditary substance lies in the nucleus) and his target (the equivalence of chromosomes). It is not drawn as a refutation, because Weismann's doctrine was not discarded as a whole: the central distinction between germ plasm and soma stood, and it was the particular hypothesis of equal chromosomes that fell.

  Link sources

  • Lilian Al-Chueyr Pereira Martins, Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis?, Genetics and Molecular Biology 22 (2), 261-272 (1999) Verified 20 Sep 2026

    The result conflicted with Weismann's theory, who believed that all chromosomes were equal (Sturtevant, 1965, p. 35).

  • Lilian Al-Chueyr Pereira Martins, Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis?, Genetics and Molecular Biology 22 (2), 261-272 (1999) Verified 20 Sep 2026

    By the late 19th century, several authors such as August Weismann and Oscar Hertwig, had already proposed that the elements responsible for transmitting hereditary characters were inside the cellular nucleus (Stubbe, 1972, pp. 160, 245).

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• 'The Chromosomes in Heredity': chromosome behaviour as the physical basis of Mendel's laws

  influenced · Confidence: medium

  The notion of a reduction division, which Weismann inferred on theoretical grounds, entered the cytological vocabulary and was used in 1902-1903 as given: it was on the separation of paternal and maternal chromosomes at the reduction division that Sutton and Wilson rested their explanation of the purity of the gametes.

  Dispute: Martins stresses that the Weismannian understanding of the reduction division as transverse was mistaken and that the cytology of those years hardly knew what happens at synapsis at all. Weismann therefore gave Sutton not a correct mechanism but a vocabulary and a way of posing the question; the descent is recorded as "influenced", not as a prerequisite.

  Link sources

  • Lilian Al-Chueyr Pereira Martins, Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis?, Genetics and Molecular Biology 22 (2), 261-272 (1999) Verified 20 Sep 2026

    A. Weismann had suggested that corresponding maternal and paternal chromosomes were joined by their ends in the process of fertilization, and that chromosomes were reduced to their primitive size in gametogenesis (during the so-called "reducing division").

  • Lilian Al-Chueyr Pereira Martins, Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis?, Genetics and Molecular Biology 22 (2), 261-272 (1999) Verified 20 Sep 2026

    The other would be a special division that "separates whole chromosomes by a transverse division (`reducing division' of Weismann)" (Wilson, 1902, p. 992). In other words, Wilson still interpreted meiosis in the old Weismannian sense.

  • Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 5 Oct 2026

    Not only did Weismann theorize that reduction division takes place, but he suggested also that a similar process to that in the maturation of the ovum could occur during spermatogenesis; this was confirmed by cytological investigation.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Other links

• Inheritance of acquired characters: the second law of the 'Philosophie zoologique'

  refuted by · Confidence: high

  Weismann declared that acquired characters are not inherited because changes of the body do not reach the germ plasm; in 1887-1888 he cut off the tails of white mice over several generations and obtained not one tailless young. He himself wrote that without the transmission of the acquired 'the Lamarckian theory completely collapses'.

  Dispute: The refutation is not held to be final by everyone. First, the mouse experiment tests only the inheritance of mutilations, not of the effects of use and disuse that Lamarck spoke of; Gauthier pointed this out (BIOS 61, 1990, as summarised in the English Wikipedia, the article itself was not read). Second, Weismann himself granted that Darwin 'to a large extent retained' the Lamarckian principle, so the blow fell on Darwin too. Third, since the 2000s epigenetic inheritance has been presented as a confirmation 'at least of a sort' of Lamarck's most famous idea; Burkhardt (2013) writes plainly that he does not take the modern studies as a vindication of Lamarck, yet grants that the argument is open. What is marked as a dead end here is the mechanism that was not found: the direct carrying of a character acquired by the body into the offspring through the use of an organ; the question of non-genetic transmission through epigenetic marks remains separate and alive.

  Link sources

  • Ruth Schwartz Cowan, Commentary: Before Weismann and germplasm there was Galton and eugenics, International Journal of Epidemiology 45 (1), 15-20 (2016) Verified 20 Sep 2026

    Weismann, one of the ablest of the German founders of cytology, is famous for having given the inheritance of acquired characters its final coup de grace by cutting off the tails of newborn laboratory mice and observing their offspring for several generations without once finding a newborn tail-less mouse.

  • Gloria Robinson, «Weismann, August Friedrich Leopold», Complete Dictionary of Scientific Biography (2008) Verified 5 Oct 2026

    He followed the results of mutilations, cutting off the tails of hundreds of mice, but without any apparent hereditary effects.

  • Gloria Robinson, «Weismann, August Friedrich Leopold», Complete Dictionary of Scientific Biography (2008) Verified 20 Sep 2026

    He decided that acquired characters could not be inherted, for to become inheritable, changes would have to affect the germ plasm itself.

  • August Weismann, On the Supposed Botanical Proofs of the Transmission of Acquired Characters (1888), Essays upon Heredity and Kindred Biological Problems, Oxford: Clarendon Press, 1889 (1889) Verified 5 Oct 2026

    For if acquired characters cannot be transmitted, the Lamarckian theory completely collapses, and we must entirely abandon the principle by which alone Lamarck sought to explain the transformation of species,

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Pangenesis: gemmules from the whole body gather in the germ cells

  refuted by · Confidence: medium

  Weismann's germ plasm cancelled the very premise of pangenesis, the flow of hereditary matter from the body to the germ cells: for Weismann heredity runs only from the germ plasm to the body. Weismann called gemmules 'a pure invention', and pangenesis, in the words of Liu and Chen, was quickly replaced by his theory.

  Dispute: The confidence is medium: the authors of the main quotation, Liu and Chen, are biologists rather than historians, and their piece argues for a 'resurrection' of pangenesis through extracellular vesicles and RNA; Robinson's DSB article speaks of the denial of inheritance of the acquired, not of pangenesis by name. Historians also differ on what exactly closed pangenesis: de Beer places the end at the rediscovery of Mendel in 1900, Julian Huxley at Morgan's chromosome theory. Moreover, pangenesis has living offspring: de Vries's 'intracellular pangenesis' (1889) kept the particles but gave up their transport from the body to the germ cells. It is that transport that is marked as the dead end, not the idea of hereditary particles.

  Link sources

  • Yongsheng Liu, Qi Chen, 150 years of Darwin's theory of intercellular flow of hereditary information, Nature Reviews Molecular Cell Biology 19 (12), 749-750 (2018) Verified 20 Sep 2026

    The Pangenesis theory was quickly replaced by Weismann’s Germ-Plasm theory, which postulated that information only flows from germ cells to somatic cells, and not vice versa (this is also known as the ‘Weismann barrier’).

  • Yongsheng Liu, Qi Chen, 150 years of Darwin's theory of intercellular flow of hereditary information, Nature Reviews Molecular Cell Biology 19 (12), 749-750 (2018) Verified 20 Sep 2026

    These speculations could not be validated at the time and were considered as “the fictions of the fancy” by the physician and microscopist Lionel Beale, and as “a pure invention” by the evolutionary biologist August Weismann.

  • Gloria Robinson, «Weismann, August Friedrich Leopold», Complete Dictionary of Scientific Biography (2008) Verified 5 Oct 2026

    He maintained that the germ plasm, the substance of heredity, was transmitted from generation to generation, distinguishing it from the somatoplasm; he also was foremost in his day in denying that acquired characters were inherited.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Node sources

• Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 5 Oct 2026

  He maintained that the germ plasm, the substance of heredity, was transmitted from generation to generation, distinguishing it from the somatoplasm; he also was foremost in his day in denying that acquired characters were inherited.

• Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 5 Oct 2026

  He followed the results of mutilations, cutting off the tails of hundreds of mice, but without any apparent hereditary effects.

• Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 5 Oct 2026

  Not only did Weismann theorize that reduction division takes place, but he suggested also that a similar process to that in the maturation of the ovum could occur during spermatogenesis; this was confirmed by cytological investigation.

• Gloria Robinson, Weismann, August Friedrich Leopold, Complete Dictionary of Scientific Biography (1976) Verified 5 Oct 2026

  Eine Theorie der Vererbung (Jena, 1892; English translation, The Germ-plasm [London, 1893]).

• Frederick B. Churchill, Weismann, August Friedrich Leopold, New Dictionary of Scientific Biography (2008) Verified 5 Oct 2026

  Never a proponent of the Lamarckian mechanism of the inheritance of acquired characters, Weismann found by the early 1880s in his demonstration of a continuity of germplasm in hydroids and in its conjectured segregation from the differentiating cells of the soma an a priori argument against such inheritance.

• August Weismann, Essays upon Heredity and Kindred Biological Problems, Oxford: Clarendon Press, 1889, VIII «The Supposed Transmission of Mutilations» (Project Gutenberg, ebook 48132) (1889) Verified 5 Oct 2026

  VIII. THE SUPPOSED TRANSMISSION OF MUTILATIONS. 1888. A lecture delivered at the Meeting of the Association of German Naturalists at Cologne, September 1888.

• August Weismann, Essays upon Heredity and Kindred Biological Problems, Oxford: Clarendon Press, 1889, VIII «The Supposed Transmission of Mutilations» (Project Gutenberg, ebook 48132) (1889) Verified 5 Oct 2026

  Thus 901 young were produced by five generations of artificially mutilated parents, and yet there was not a single example of a rudimentary tail or of any other abnormity in this organ.

"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

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