On parthenogenesis, a discourse introductory to the Hunterian lects. on generation and development, 18491849 |
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Página 9
... accessory and non - essential part . The very small size in relation to the entire body , and the superficial position , of the derivative germ - cell which takes on the processes of development in the Hydra , appear 9.
... accessory and non - essential part . The very small size in relation to the entire body , and the superficial position , of the derivative germ - cell which takes on the processes of development in the Hydra , appear 9.
Página 12
... take on a higher form , resembling that of a bell - shaped Medusa ; they become detached and swim off to a distance , forming and discharging the ova , which , as Steenstrup conjectures , in their turn develope the fixed polype - shaped ...
... take on a higher form , resembling that of a bell - shaped Medusa ; they become detached and swim off to a distance , forming and discharging the ova , which , as Steenstrup conjectures , in their turn develope the fixed polype - shaped ...
Página 40
... take place agreeably with the law of alternate gene- ration , " and the metaphorical comparison of the Hydra and Strobila with ' wet - nurses ' ( Ammen ) , bring no in- formation as to the organic conditions of the phænomena : the facts ...
... take place agreeably with the law of alternate gene- ration , " and the metaphorical comparison of the Hydra and Strobila with ' wet - nurses ' ( Ammen ) , bring no in- formation as to the organic conditions of the phænomena : the facts ...
Página 46
... take the place of the former ; and by the repetition of this increase and multiplication a long and single series of tubular cells , attached at one end , free and constantly growing at the other , is at last produced , as Unger and ...
... take the place of the former ; and by the repetition of this increase and multiplication a long and single series of tubular cells , attached at one end , free and constantly growing at the other , is at last produced , as Unger and ...
Página 58
... takes place , with manifold modifications , but essentially by the multiplication of cells , according to a process which is as much entitled to be called continuous growth as that process in the formation of the Conferva . The embryo ...
... takes place , with manifold modifications , but essentially by the multiplication of cells , according to a process which is as much entitled to be called continuous growth as that process in the formation of the Conferva . The embryo ...
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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...