The Doctrine of Descent and DarwinismD. Appleton, 1875 - 334 páginas |
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Página 44
... ovum and the sperm . The ovum is always , in the first in- stance , a simple cell , of which the nucleus is termed the germinal vesicle , and the nucleole the germinal spot . In many animals it is provided with a sheath or 44 THE ...
... ovum and the sperm . The ovum is always , in the first in- stance , a simple cell , of which the nucleus is termed the germinal vesicle , and the nucleole the germinal spot . In many animals it is provided with a sheath or 44 THE ...
Página 45
... lutionists and Epigenists has now a merely historical interest . The former maintained that either in the ovum or in the sperm - corpuscle the whole future organism was prefigured in all its parts , and that it GERM - CELLS . 45.
... lutionists and Epigenists has now a merely historical interest . The former maintained that either in the ovum or in the sperm - corpuscle the whole future organism was prefigured in all its parts , and that it GERM - CELLS . 45.
Página 46
... ovum the yet undifferentiated material which subsequent to fecundation had still to be transformed into the various morphological elements and organs . But it is scarcely twenty years ago since the process of fecunda- tion was ...
... ovum the yet undifferentiated material which subsequent to fecundation had still to be transformed into the various morphological elements and organs . But it is scarcely twenty years ago since the process of fecunda- tion was ...
Página 49
... probable that among all embryos of verte- brate , as well as invertebrate animals , developed from a true ovum , there is a conformity in the condition of the germ at a period when the type has not yet TYPES OF DEVELOPMENT . 49.
... probable that among all embryos of verte- brate , as well as invertebrate animals , developed from a true ovum , there is a conformity in the condition of the germ at a period when the type has not yet TYPES OF DEVELOPMENT . 49.
Página 52
... deeper foundation for the existence of these types . We will illustrate our meaning by two examples . When the ovum of the articulate animal has sur- f rounded itself with a germinal membrane , a portion 52 THE DOCTRINE OF DESCENT .
... deeper foundation for the existence of these types . We will illustrate our meaning by two examples . When the ovum of the articulate animal has sur- f rounded itself with a germinal membrane , a portion 52 THE DOCTRINE OF DESCENT .
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Palavras e frases frequentes
according adaptation already Ammonites Amphibians animal world apes appearance Ascidian birds body bone brain causes Cetacea character characteristics comparative anatomy complete connection continent Darwin dentition derivation diverge doctrine of Descent Echinoderms embryo Eocene exhibit existence external facts families fauna fish formation fossil Gastrula gemmules genera genus geological Goethe grade gradually groups Haeckel heredity higher horse human hypothesis idea individual infer intermediate forms investigation islands lancelet language larva larvæ likewise linguistic lower mammals Marsupials Medusa ment merely metamorphosis modifications morphological mutability natural selection observations Oolite organisms origin ovum peculiar pedigree perfect period phase phenomena placenta plants polypes possess present primordial progenitors races regard relations remains reproduction reptiles Rütimeyer says scarcely scientific separate sexual Silurian skull species strata structure systematic terrestrial animals theory of selection tion transformation true Ungulata Ungulates varieties vertebral column Vertebrata vertebrate animals whole