On parthenogenesis, a discourse introductory to the Hunterian lects. on generation and development, 18491849 |
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Página 4
... germinal vesicle , ' and is the essential part of the ovum ; the other nucleated cell is the ' sperm - cell , ' and its product is the spermatozoon . It is essential to the development of the germ that the ovum receive the matter of the ...
... germinal vesicle , ' and is the essential part of the ovum ; the other nucleated cell is the ' sperm - cell , ' and its product is the spermatozoon . It is essential to the development of the germ that the ovum receive the matter of the ...
Página 38
... germinal vesicle as in the oviparous females . The most marked and essential di- stinction , however , between the generative organs of these two kinds of female is the multilocular form of the uterus and simple vagina in the viviparous ...
... germinal vesicle as in the oviparous females . The most marked and essential di- stinction , however , between the generative organs of these two kinds of female is the multilocular form of the uterus and simple vagina in the viviparous ...
Página 39
... germinal vesicles , that the stimulus of a new coitus is requisite to set on foot the developmental processes . In the Aphis , on the contrary , the presence of such common external stimuli as warmth , light and nutriment suffice to ...
... germinal vesicles , that the stimulus of a new coitus is requisite to set on foot the developmental processes . In the Aphis , on the contrary , the presence of such common external stimuli as warmth , light and nutriment suffice to ...
Página 43
... germinal vesicle which is developed into an egg in the wedded oviparous Aphis . In this , when impregnated , a germ - mass must be formed , identical in character with the foregoing , prior to embryonic formation . The first steps of ...
... germinal vesicle which is developed into an egg in the wedded oviparous Aphis . In this , when impregnated , a germ - mass must be formed , identical in character with the foregoing , prior to embryonic formation . The first steps of ...
Página 51
... germinal mass in the ovum , he might have arrived at the desired explanation ; but he affirms them to be altogether distinct . ' 6 Admitting the obvious analogies between the reproduc- tive phænomena of the Medusa and the Plant , Dr ...
... germinal mass in the ovum , he might have arrived at the desired explanation ; but he affirms them to be altogether distinct . ' 6 Admitting the obvious analogies between the reproduc- tive phænomena of the Medusa and the Plant , Dr ...
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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...