An Examination of WeismannismOpen Court Publishing Company, 1893 - 221 pages |
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Common terms and phrases
a-sexual absolute stability acquired characters admixtures amphimixis ancestral appears assumption atavism become carriers of heredity cause chapter chromatin congenital variations constitute continuity of germ-plasm Darwin distinction doctrine Essays evidence external conditions fact fertilized fundamental postulate Galton gemmules germ-cells germinal elements Hence hypothesis idio-plasm important individual variations influence inherited kind Lamarckian factors logical matter Metazoa modified molecules multicellular organisms natural selection nuclear nucleo-plasm nucleus occur ontogenetic ontogeny organic evolution origin of sexual ovum parents parthenogenetic perpetual continuity phenomena physiological plants plasm polar body present previous sire produced Professor Vines Professor Weismann progeny Protozoa prove question regard reproductive cells result sexual propagation sexual reproduction sexual union soma somatic cells somatic tissues somatic-cells somatic-tissues somato-plasm somatogenetic species spermatozoa stability of germ-plasm stirp substance of heredity supposed theory of evolution theory of germ-plasm theory of heredity theory of pangenesis tion transmission of acquired unicellular organisms Weismann's theory
Popular passages
Page 3 - ... which these two packets contain. 5. That a large proportional number of the gemmules in each packet, however, fail to develop, and are then transmitted in a dormant state to future generations, in any of which they may be developed subsequently, thus giving rise to the phenomena of reversion or atavism. 6. That in all cases the development of gemmules into the form of their parent cells depends on their suitable union with other partially developed gemmules which precede them in the regular course...
Page 192 - I tried to breed from the male quagga and a young chestnut mare of seven-eighths Arabian blood, and which had never been bred from: the result was the production of a female hybrid, now five years old, and bearing, both in her form and in her colour, very decided indications of her mixed origin.
Page 202 - They prove that while the reproductive cells multiply and arrange themselves during the evolution of the embryo, some of their germ-plasm passes into the mass of somatic cells constituting the parental body, and becomes a permanent component of it. Further, they necessitate the inference that this introduced germ-plasm, everywhere diffused, is some of it included in the reproductive cells subsequently formed.
Page 10 - Weismann has shown, by a somewhat laborious though still largely imperfect research, that there is throughout all the metazoa a general correlation between the natural lifetime of individuals composing any given species and the age at which they reach maturity, or first become capable of procreation. This general correlation, however, is somewhat modified by the time during which progeny are dependent upon their parents for support and protection. Nevertheless, it is evident that this modification...
Page 204 - Professor Marsh, the distinguished palaeontologist, of Yale, New Haven, who is also collecting evidence, sends a preliminary letter in which he says : — " I do not myself know of such a case, but have heard many statements that make their existence probable. One instance, in Connecticut, is vouched for so strongly by an acquaintance of mine, that I have good reason to believe it to be authentic.
Page 194 - ... to life in that locality : the result being that in the development of each young individual, the tendencies conspire to produce the fit organization. It is otherwise when the species is removed to a habitat of different character, or when it is of mixed breed. In the one case its organs, partially out of harmony with the requirements of its new life, become partially out of harmony with one another ; since, while one influence, say of climate, is but little changed, another influence, say of...
Page 195 - ... house of which the members are in concord. Now if this is shown to be the case with breeds the purest of which have been adapted to their habitats and modes of life during some few hundred years only, what shall we say when the question is of a breed which has had a constant mode of life in the same locality for ten thousand years or more, like the quagga? In this the stability of constitution must be such as no domestic animal can approach. Relatively stable as may have been the constitutions...
Page 196 - ... litter. Mr. Giles adds that in a second litter of pigs, the father of which was of Mr. Western's breed, he and his bailiff believe there was a recurrence, in some, of the chestnut colour, but admits that their "recollection is much less perfect than I wish it to be.
Page 194 - Still more in the other case is there a disturbance in equilibrium. In a mongrel, the constitution derived from each source repeats itself as far as possible. Hence a conflict of tendencies to evolve two structures more or less unlike. The tendencies do not harmoniously conspire, but produce partially incongruous sets of organs. And evidently where the breed is one in which there are united the traits of various lines of ancestry, there results an organization so full of small incongruities of structure...
Page 206 - Dr. Romanes urges, is the inconceivability of the process by which the germ-plasm of a preceding male parent affects the constitution of the female and her subsequent offspring. In response. I have to ask why he piles up a mountain of difficulties based on the assumption that Mr. Darwin's explanation of heredity by " Pangenesis " is the only available explanation preceding that of Weibinaun ? and why he presents these difficulties to me, more especially ; deliberately ignoring my own hypothesis of...