Heredity / by J. Arthur Thomson.

  • Thomson, J. Arthur (John Arthur), 1861-1933.
Date:
1908
Catalogue details

Licence: In copyright

Credit: Heredity / by J. Arthur Thomson. Source: Wellcome Collection.

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

    92/668 (page 62)
    62 THE PHYSICAL BASIS OF INHERITANCE equal distribution of paternal and maternal chromatin to all the cells of the offspring, we find the physiological explanation of the fact that every part of the latter may show the characteristics of either or both parents (Wilson, 1900, P- 352). 4. Arg^ment from Boveri's ingenious experiment.—Taking a hint from the experiments of the brothers Hertwig, who showed that non-nucleated fragments of unfertilised sea-urchin ova (broken by shaking) might be successfully fertilised and might segment, Boveri (1889, ^^95) showed that such fertihsed frag- ments developed into dwarf, but normal, larvse. In these, as T. H. Morgan (1895) afterwards showed, the nuclei contain only half the normal number of chromosomes, having had only a sperm-nucleus to start with. Interesting as this was, Boveri's further experiment was yet more striking. He fertilised the enucleated egg-fragments of one species of sea-urchin {Sphcerechinus granularis) with sperma- tozoa of another species {Echinus microtuberculatus), and ob- tained in a few cases dwarf larvse (plutei), which showed, except as regards size, the paternal characters only. Therefore he concluded that the nucleus is the exclusive bearer of the here- ditary qualities, for it seemed from the experiment that the enucleated maternal cytoplasm had remained without specific influence. It is admitted by Boveri himself that further experiments are necessary, and it must be granted also, as has been pointed out by Seeliger, Morgan, and Driesch, that in cases of hybridism, as in Boveri's experiment, there may be a marked illustration of what is called unilateral or preponderant inheritance. While most hybrids are intermediate, some take after the father and others after the mother. But the experiment remains uncontroverted, if unsubstantiated, and it is as suggestive as it was ingenious. Generally accepted Conclusion—The general conclusion