The Evolution Theory, Vol. 2 of 2

The Evolution Theory, Vol. 2 of 2

Budding and divisionEvery theory of regeneration in the meantime only provisional, a mere 'portmanteau theory'Regeneration not a primary characterVolvoxHydraVital affinitiesPlanariansHeteromorphosesEnemies of Hydroid-coloniesRegeneration in PlantsIn AmphibiansIn EarthwormsDifferent degrees of regenerative capacity according to the liability of the part to injuryDifferent results of longitudinal halving in Earthworms and in PlanariansRegeneration in BirdsThe disappearance of the power of regeneration is very slowMorgan's experiments on Hermit-crabsAutotomy in Crustaceans and InsectsRegeneration of the lens in Triton. We have endeavoured to explain the handing on of the complement of heritable qualities from one generation to another as due to a continuity of the germ-plasm, and we assumed that the germ-cells never arise except from cells in the 'germ-track'; that is, from cells which are equipped, from the fertilized egg-cell onwards, with a complete sample of slumbering germ-plasm, and are thereby enabled to become germ-cells, and, subsequently, new individuals, in which the aggregate of inherited primary constituents implied in the germ-plasm can again attain to development. For both these cases the germ-plasm theory will suffice, with a somewhat modified form of the same assumption which we made in regard to the formation of germ-cells. The origin of a new individual by budding seems often, indeed, to proceed from any set of somatic cells in the mother animal; but somatic cells, if they contain solely the determinants controlling themselves, cannot possibly give rise to a complete new individual, since this presupposes the presence of all the determinants of the species. But as these determinants cannot be formed de novo, the budding cells must contain in addition to the usual controlling somatic determinants, idioplasm in a latent, inactive state, which only becomes active under certain internal or external influences, and then gives rise to the formation of a bud. The source[Pg 2] of this accessory idioplasm must, however, be looked for only in the egg-cell. ......Buy Now (To Read More)

Product details

Ebook Number: 65049
Author: Weismann, August
Release Date: Apr 10, 2021
Format: eBook
Language: English

Contributors

Translator: Thomson, J. Arthur (John Arthur), 1861-1933, Thomson, Margaret R.