On parthenogenesis, a discourse introductory to the Hunterian lects. on generation and development, 18491849 |
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Página 8
... centres . So much of the primary de- velopmental processes is renewed , as leads to the insulation . of the sphere of the influence of each assimilative centre from that of the other by the progressive formation of the final subdivision ...
... centres . So much of the primary de- velopmental processes is renewed , as leads to the insulation . of the sphere of the influence of each assimilative centre from that of the other by the progressive formation of the final subdivision ...
Página 9
... centre of assimilation is first formed , which soon opens into the stomach of the parent : but the communication is afterwards closed , and the young Hydra is ultimately cast off from the surface of the parent . This mode of propagation ...
... centre of assimilation is first formed , which soon opens into the stomach of the parent : but the communication is afterwards closed , and the young Hydra is ultimately cast off from the surface of the parent . This mode of propagation ...
Página 10
... centre from which all the processes in the formation of the new individual radiate . The Hydra propagates by ova as well as by buds . Cer- tain of the retained fertile germ - cells multiply themselves , and coalesce to form a larger ...
... centre from which all the processes in the formation of the new individual radiate . The Hydra propagates by ova as well as by buds . Cer- tain of the retained fertile germ - cells multiply themselves , and coalesce to form a larger ...
Página 15
... centres of the nuclear matter into numerous independent germ - masses , and their de- velopment into embryos : these are first manifested by the appearance of an anterior and a median circular sucker , and then they acquire cephalic ...
... centres of the nuclear matter into numerous independent germ - masses , and their de- velopment into embryos : these are first manifested by the appearance of an anterior and a median circular sucker , and then they acquire cephalic ...
Página 18
... centre of the cili- ated embryo or modified germ - mass . In that aggregated * Isis von Oken , 1818 , p . 729 . ↑ Beiträge zur Kenntniss der Niederen Thiere , Nova Acta Leop . Car . tom . xiii . pt . ii . p . 629 . ‡ Beitrag zur ...
... centre of the cili- ated embryo or modified germ - mass . In that aggregated * Isis von Oken , 1818 , p . 729 . ↑ Beiträge zur Kenntniss der Niederen Thiere , Nova Acta Leop . Car . tom . xiii . pt . ii . p . 629 . ‡ Beitrag zur ...
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On Parthenogenesis, a Discourse Introductory to the Hunterian Lects. on ... Richard Owen (sir ) Sin vista previa disponible - 2019 |
Términos y frases comunes
aggregate alternate analogy animal animalcule Annelides Aphides appendages assimilation body called Cercariæ cercariform chorion ciliated coalesce continuous growth Coryne Dalyell derivative germ-cells detached distinct Distoma division Echinus Ehrenberg embryo Entozoa Entozoon essential condition explain fact flower fluid formation gemmiparous germ germ-cells and nuclei germ-mass germ-yelk germinal vesicle granular Gregarina gregariniform Hydra Hydra Tuba impregnated ovum individual insects integument Kölliker larvæ larval Aphis larviparous Aphis leaf limbs Medusa medusiform ment metamorphosed mode modifications monad monadiform multiplication of cells nature nucleated cells nucleus nutriment observed organs ovarian oviparous oviparous females ovum parent Parthenogenesis pellucid centre phænomena physiologist phytons plant planulæ Pluteus Polygastria polype pregnated primary impregnated germ-cell procreation produced Prof progeny propagated by gemmation resemble result retained Scyphistoma secondary germ-cell Siebold species spermatheca spermatic force spermatic virtue spermatozoon spontaneous fission stamen Steenstrup Strobila successive tion tissues trematode unchanged virgin viviparous wet-nurse yelk zoophyte
Pasajes populares
Página 33 - ... and, what is most remarkable and without parallel, the sexual intercourse of one original pair serves for all the generations which proceed from the female for a whole succeeding year. Reaumur has proved that in five generations one Aphis may be the progenitor of 5,904,900,000 descendants ; and it is supposed that in one year there may be twenty...
Página 22 - Assuredly, there is more birth and death in the world than is dreamt of by the greater part of us; but it is so masked, and on the whole, so little to our purpose, that we fail to see it.
Página 56 - ... repeats the process ; and it may be again repeated in the same geometrical ratio until a number which figures only can indicate and language almost fails to express, is the result. The Aphides...
Página 41 - Owen does not recognize any physiological difference between a bud and an ovum. This is clear from what he remarks in the first quotation ; but in his work on Parthenogenesis he has said so in as many words. " The growth by cell-multiplication producing a bud, instead of being altogether distinct from the growth by cell-multiplication in an egg, is essentially the same kind of growth or developmental process.
Página 25 - One conjunction of the sexes suffices for the impregnation of all the females that in a succession of generations spring from that union." In support of the reasonableness of this hypothesis, they quote several instances which they regard as of analogous character ; thus, they say in regard to the hive-bee, that " a single intercourse with the male fertilizes all the eggs that are laid for the space of two years.
Página 1 - Not all the progeny of the primary impregnated germcell are required for the formation of the body in all animals : certain of the derivative germ-cells may remain unchanged and become included in that body which has been composed of their metamorphosed and diversely combined or confluent brethren : so included, any derivative germ-cell or the nucleus of such may commence and repeat the same processes...
Página 30 - Alternation of Generations^ is the remarkable phenomenon of an animal producing an offspring which at no time resembles its parent, but which, on the other hand, itself brings forth a progeny which returns in its form and nature to the parent...
Página 21 - The whole peripheral stratum of the retained germ-mass in contact with the primary integument is transformed into a new integument. These germ-cells have increased and propagated at the expense of the aliment assimilated by the alimentary canal. The formation of the new integument and of the new feet proceeds connectedly and contemporaneously : but the new parts are not moulded upon the inner surface of the old ones. The plastic force has changed its course of operation. A hinder segment of the body...