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acquired characters Actinozoa adult alimentary ancestral Annelid ants appear archenteron assume become blastopore body canal cavity ccelom changes chromatin coelom colour connection corpuscles degeneration dentary derived determinants deviation differentiation diploblastic disuse division Echinoderm eggs embryo endoderm essay evolution excretory existence explanation fact females fibres formation frontal breadth germ germ-plasm growth homologous horse hybrid hypothesis important insects instance instincts larva legs less males mare mean mesoblast Metazoa modified morphological mouth and anus natural selection nephridia nervous system neural nucleus number of glands nutrition observations occur ontogeny organs origin ovum Panmixia Peripatus plants plasm pores pouches present primitive streak principle produced Professor Weismann protoplasm Protozoa recognised regard reproductive cells result Schwann Sedgwick segmentation nucleus somites specialised species Spencer stage stomodaeum structure substance supposed telegony theory tion tissues transmission of acquired unicellular variability variations Vertebrata Vertebrate workers yolk zebra
Página 71 - The elementary parts of all tissues are formed of cells in an analogous, though very diversified manner, so that it may be asserted, that there is one universal principle of development for the elementary parts of organisms, however different, and that this principle is the formation of cells.