Show results per page.
Search Help New search
Sort by
Results 1-25 of 25 for « +(+text:stage +text:embryo +text:similar) »
    Page 1 of 1. Go to page:    
38%
A586    Book:     Lindley, John. 1853. The vegetable kingdom; or, the structure, classification, and uses of plants, illustrated upon the natural system. 3d ed. London: Bradbury & Evans.   Text   Image
approaching to black. It is to this stage or period that the descriptions of those authors who attribute a style and stigma to this genus apparently refer. Both Dr. Brown and Professor Lindley must likewise advert to this period when they state the nucleus to be surrounded with three envelopes. There can be no doubt, then, that in reality Gnetum is as truly naked-eeeded as Conifers themselves. Independently of the singular organisation of its ovule, the genus Gnetum is remarkable for some other
68%
A243    Periodical contribution:     Lubbock, John. 1857. An Account of the Two Methods of Reproduction in Daphnia, and of the Structure of the Ephippium. Communicated by Charles Darwin. Philosophical Transactions of the Royal Society of London 147: 79-100.   Text   Image
developed from each side of anterior part of the embryo at this stage, and these, as well as the body and the bifurcate or fin-like caudal extremity, become invested by a delicate transparent membrane. Up to this point the embryo has been included within the vitelline membrane; but the latter is now burst, and the embryo straightening itself assumes the pear-like form described by RATHKE and by FREY and LEUCKART, as the first condition of the embryo these observers having overlooked the earlier
100%
F373    Book:     Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st edition, 1st issue.   Text   Image   PDF
fed by their parents or placed in the midst of proper nutriment, yet nearly all pass through a similar worm-like stage of development; but in some few cases, as in that of Aphis, if we look to the admirable drawings by Professor Huxley of the development of this insect, we see no trace of the vermiform stage. How, then, can we explain these several facts in embryology,—namely the very general, but not universal difference in structure between the embryo and the adult;—of parts in the same
68%
F373    Book:     Darwin, C. R. 1859. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 1st edition, 1st issue.   Text   Image   PDF
modification carried on for many generations, having to provide for their own wants at a very early stage of development, and secondly, from their following exactly the same habits of life with their parents; for in this case, it would be indispensable for the existence of the species, that the child should be modified at a very early age in the same manner with its parents, in accordance with their similar habits. Some further explanation, however, of the embryo not undergoing any metamorphosis is
42%
A507    Review:     Anon. 1859. Charles Darwin on the origin of species. Chambers's Journal 11: 388-391.   Text   Image
embryo and the adult; of parts in the same individual embryo, which ultimately become very unlike, and serve for diverse purposes, being at this early period of growth alike; of embryos of different species within the same class, generally, but not universally, resembling each other; of the structure of the embryo not being closely related to its conditions of existence, except when the embryo becomes at any period of life active, and has to provide for itself; of the embryo apparently having
95%
F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d edition, second issue.   Text   Image   PDF
adult: thus Owen has remarked in regard to cuttle-fish, there is no metamorphosis; the cephalopodic character is manifested long before the parts of the embryo are completed; and again in spiders, there is nothing worthy to be called a metamorphosis. The larvæ of insects, whether adapted to the most diverse and active habits, or quite inactive, being fed by their parents or placed in the midst of proper nutriment, yet nearly all pass through a similar worm-like stage of development; but in
89%
F380    Book:     Darwin, C. R. 1860. The origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. New York: D. Appleton. New edition, revised and augmented.   Text   Image   PDF
ment, yet nearly all pass through a similar worm-like stage of development; but in some few cases, as in that of Aphis, if we look to the admirable drawings by Professor Huxley of the development of this insect, we see no trace of the vermiform stage. How, then, can we explain these several facts in embryology, namely the very general, but not universal difference in structure between the embryo and the adult; of parts in the same individual embryo, which ultimately become very unlike and
78%
F376    Book:     Darwin, C. R. 1860. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 2d edition, second issue.   Text   Image   PDF
of development, and secondly, from their following exactly the same habits of life with their parents; for in this case, it would be indispensable for the existence of the species, that the child should be modified at a very early age in the same manner with its parents, in accordance with their similar habits. Some further explanation, however, of the embryo not undergoing any metamorphosis is perhaps requisite. If, on the other hand, it profited the young to follow habits of life in any
64%
F380    Book:     Darwin, C. R. 1860. The origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. New York: D. Appleton. New edition, revised and augmented.   Text   Image   PDF
degree different from those of their parent, and consequently to be constructed in a slightly different manner, then, on the principle of inheritance at corresponding ages, the active young or larv might easily be rendered by natural selection different to any conceivable extent from their parents. Such differences might, also, become correlated with successive stages of development; so that the larv , in the first stage, might differ greatly from the larv in the second stage, as we have seen
58%
F380    Book:     Darwin, C. R. 1860. The origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. New York: D. Appleton. New edition, revised and augmented.   Text   Image   PDF
again to cirripedes: the larv in the first stage have three pairs of legs, a very simple single eye, and a probosciformed mouth, with which they feed largely, for they increase much in size. In the second stage, answering to the chrysalis stage of butterflies, they have six pairs of [page] 38
54%
F380    Book:     Darwin, C. R. 1860. The origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. New York: D. Appleton. New edition, revised and augmented.   Text   Image   PDF
in the same manner with its parents, in accordance with their similar habits. Some further explanation, however, of the embryo not undergoing any metamorphosis is perhaps requisite. If, on the other hand, it profited the young to follow habits of life in any [page] 39
95%
F381    Book:     Darwin, C. R. 1861. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 3d edition. Seventh thousand.   Text   Image   PDF
is no metamorphosis; the cephalopodic character is manifested long before the parts of the embryo are completed; and again in spiders, there is nothing worthy to be called a metamorphosis. The larvæ of insects, whether adapted to the most diverse and active habits, or quite inactive, being fed by their parents or placed in the midst of proper nutriment, yet nearly all pass through a similar worm-like stage of development; but in some few cases, as in that of Aphis, if we look to the admirable
78%
F381    Book:     Darwin, C. R. 1861. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 3d edition. Seventh thousand.   Text   Image   PDF
child should be modified at a very early age in the same manner with its parents, in accordance with their similar habits. Some further explanation, however, of the embryo not undergoing any metamorphosis is perhaps requisite. If, on the other hand, it profited the young to follow habits of life in any degree different from those of their parent, and consequently to be constructed in a slightly different manner, then, on the principle of inheritance at corresponding ages, the active young or larvæ
45%
F381    Book:     Darwin, C. R. 1861. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 3d edition. Seventh thousand.   Text   Image   PDF
are in the embryo exactly alike. The embryos, also, of distinct animals within the same class are often strikingly similar: a better proof of this cannot be given, than a statement made by Von Baer, namely, that the embryos of mammalia, of birds, lizards, and snakes, probably also of chelonia, are in their earliest states exceedingly like one another, both as a whole and in the mode of development of their parts; so much so, in fact, that we can often distinguish the embryos only by their size
97%
F385    Book:     Darwin, C. R. 1866. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 4th edition. 8th thousand.   Text   Image   PDF
in the midst of proper nutriment or fed by their parents, yet nearly all pass through a similar worm-like stage of development; but in some few cases, as in that of Aphis, if we look to the admirable drawings by Professor Huxley of the development of this insect, we see hardly any trace of the vermiform stage. In some cases it is only the earlier developmental stages which fail; these apparently having been suppressed. Thus Fritz M ller has recently made the remarkable discovery that certain
53%
F877.2    Book:     Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st edition, first issue. Volume 2   Text   Image   PDF
the expression of La loi de l'affinité de soi pour soi. It has been fully discussed and illustrated by his son, Isidore Geoffroy, with respect to monsters in the animal kingdom,1 and by Moquin-Tandon, with respect to monstrous plants. When similar or homologous parts, whether belonging to the same embryo or to two distinct embryos, are brought during an early stage of development into contact, they often blend into a single part or organ; and this complete fusion indicates some mutual affinity
53%
F878.2    Book:     Darwin, C. R. 1868. The variation of animals and plants under domestication. London: John Murray. 1st edition, second issue. Volume 2.   Text   Image   PDF
of La loi de l'affinit de soi pour soi. It has been fully discussed and illustrated by his son, Isidore Geoffroy, with respect to monsters in the animal kingdom,1 and by Moquin-Tandon, with respect to monstrous plants. When similar or homologous parts, whether belonging to the same embryo or to two distinct embryos, are brought during an early stage of development into contact, they often blend into a single part or organ; and this complete fusion indicates some mutual affinity between the
38%
F880.2    Book:     Darwin, C. R. 1875. The variation of animals and plants under domestication. London: John Murray. 2d edition. Volume 2.   Text   Image   PDF
of lesser anomalies are admitted by every one to be due to an arrest of development, that is, to the persistence of an embryonic condition. But many monstrosities cannot be thus explained; for parts of which no trace can be detected in the embryo, but which occur in other members of the same class of animals occasionally appear, and these may probably with truth be attributed to reversion. As, however, I have treated this subject as fully as I could in my 'Descent of Man' (chap. i., 2nd edit
53%
A39    Book:     Hird, D. 1903. An easy outline of evolution. London, Watts & Co.   Text   Image
line, not only between the plant and animal kingdom, but between the kingdoms of the living and the not-living. It is impossible to give all the details, but we will notice a few. 1.To begin with the very small cell, called the ovum or germ. After impregnation the cell divides into two, four, eight, sixteen, thirty-two, and so forth, until a mass of similar cells is formed. This stage of the human animal is called the morula stage. Morus means a mulberry, and the E [page] 4
38%
F1548.1    Book:     Darwin, Francis & Seward, A. C. eds. 1903. More letters of Charles Darwin. A record of his work in a series of hitherto unpublished letters. London: John Murray. Volume 1   Text   Image   PDF
creatures of the simplest organisations mainly multiply by some process of self-division. 1. Mr. Galton's idea is that in a bud or other asexually produced part, the germs (i.e. gemmules) may not be completely representative of the whole organism, and if reproduction is continued asexually at each successive stage there is always a chance of some one or more of the various species of germs... dying out (page 333). Mr. Galton supposes, in sexual reproduction, where two parents contribute germs to the
56%
A162    Book:     Seward, A. C. ed. 1909. Darwin and modern science. Essays in commemoration of the centenary of the birth of Charles Darwin and of the fiftieth anniversary of the publication of The origin of species. Cambridge: Cambridge University Press.   Text   Image   PDF
? The reason is clearly this, that budding usually occurs after the embryonic stage is past; when the characters of embryonic life have been worked out by the machine. When it takes place at an early stage in embryonic life, as it does in cases of so-called embryonic fission, the product shows, either partly or entirely, phenomena similar to those of embryonic development. The only case known to me in which budding by the adult is accompanied by morphological features similar to those displayed
52%
A162    Book:     Seward, A. C. ed. 1909. Darwin and modern science. Essays in commemoration of the centenary of the birth of Charles Darwin and of the fiftieth anniversary of the publication of The origin of species. Cambridge: Cambridge University Press.   Text   Image   PDF
formed, that is to those positions towards which the longitudinal halves of the chromosomes travel in ordinary nuclear divisions. It is clear that in this way the number of chromosomes which the daughter-nuclei contain, as the result of the first stage in division in the gonotokonts, will be reduced by one half, while in ordinary divisions the number of chromosomes always remains the same. The first stage in the division of the nucleus in the gonotokonts has therefore been termed the reduction
50%
A162    Book:     Seward, A. C. ed. 1909. Darwin and modern science. Essays in commemoration of the centenary of the birth of Charles Darwin and of the fiftieth anniversary of the publication of The origin of species. Cambridge: Cambridge University Press.   Text   Image   PDF
generalisation known as the Law of v. Baer. The law asserts that embryos of different species of animals of the same group are more alike than the adults and that, the younger the embryo, the greater are the resemblances. If this law could be established it would undoubtedly be a strong argument in favour of the recapitulation explanation of the facts of embryology. But its truth has been seriously disputed. If it were true we should expect to find that the embryos of closely similar species
45%
A162    Book:     Seward, A. C. ed. 1909. Darwin and modern science. Essays in commemoration of the centenary of the birth of Charles Darwin and of the fiftieth anniversary of the publication of The origin of species. Cambridge: Cambridge University Press.   Text   Image   PDF
differ from each other in structure and habits in their adult condition, if they pass through closely similar embryonic stages, we may feel assured that they all are descended from one parent-form, and are therefore closely related. Thus, community in embryonic structure reveals community of descent; but dissimilarity in embryonic development does not prove discommunity of descent, for in one of two groups the developmental stages may have been suppressed, or may have been so greatly modified
44%
A162    Book:     Seward, A. C. ed. 1909. Darwin and modern science. Essays in commemoration of the centenary of the birth of Charles Darwin and of the fiftieth anniversary of the publication of The origin of species. Cambridge: Cambridge University Press.   Text   Image   PDF
they will assimilate more feebly and grow more slowly, unless chance streams of nutriment help them to recover themselves. But, as will presently be shown, a change of direction cannot take place at every stage of the degenerative process. If a certain critical stage of downward progress be passed, even favourable conditions of food-supply will no longer suffice permanently to change the direction of the variation. Only two cases are conceivable; if the determinant corresponds to a useful organ
    Page 1 of 1. Go to page: