On parthenogenesis, a discourse introductory to the Hunterian lects. on generation and development, 18491849 |
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Página 8
... propagating , as if it were a completed individual , usually under a form very different from that which itself or its progeny are destined ultimately to assume ; whence these arrested forms have been termed ' Larvæ , ' the true ...
... propagating , as if it were a completed individual , usually under a form very different from that which itself or its progeny are destined ultimately to assume ; whence these arrested forms have been termed ' Larvæ , ' the true ...
Página 10
... propagates by ova as well as by buds . Cer- tain of the retained fertile germ - cells multiply themselves , and ... propagate by buds , and the Hydra so de- veloped may propagate again by ova , and these two kinds of generation may ...
... propagates by ova as well as by buds . Cer- tain of the retained fertile germ - cells multiply themselves , and ... propagate by buds , and the Hydra so de- veloped may propagate again by ova , and these two kinds of generation may ...
Página 11
... propagate by ova , in order that the spe- cies may be dispersed . In some species the germ - cells are metamorphosed into ova at particular parts , and the con- comitant growth of the soft tissue and outer crust furnishes those ova with ...
... propagate by ova , in order that the spe- cies may be dispersed . In some species the germ - cells are metamorphosed into ova at particular parts , and the con- comitant growth of the soft tissue and outer crust furnishes those ova with ...
Página 14
... propagates by gemmation . The condition of this Parthenogenesis , ' or power of propagation by the virgin larval ... propagate by gemmation and spontaneous fission . and spermatozoa are developed ; in others , ovisacs and 14.
... propagates by gemmation . The condition of this Parthenogenesis , ' or power of propagation by the virgin larval ... propagate by gemmation and spontaneous fission . and spermatozoa are developed ; in others , ovisacs and 14.
Página 15
... propagated by gemmation under the latter form are ultimately resolved by spontaneous fission into the male or female oviparous Medusa . I will cite a few other instances in which a species is represented by a series of individuals of ...
... propagated by gemmation under the latter form are ultimately resolved by spontaneous fission into the male or female oviparous Medusa . I will cite a few other instances in which a species is represented by a series of individuals of ...
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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...