The cell in development and inheritance . B. Fig. 4. — Cleavage of the ovum of the sea-urchin Toxopticustes, x 330, from life. The suc-cessive divisions up to the i6-cell stage (//) occupy about two hours. / is a section of tlie embryo(blastula) of three hours, consisting of approximately 128 cells surrounding a central cavity orblastoccel. tion take the facts of variation and heredity as fundamental postulates,for it is by variation that new characters arise and by heredity thatthey are perpetuated. Darwin recognized two kinds of variation,both of which, being inherited and maintained through
The cell in development and inheritance . B. Fig. 4. — Cleavage of the ovum of the sea-urchin Toxopticustes, x 330, from life. The suc-cessive divisions up to the i6-cell stage (//) occupy about two hours. / is a section of tlie embryo(blastula) of three hours, consisting of approximately 128 cells surrounding a central cavity orblastoccel. tion take the facts of variation and heredity as fundamental postulates,for it is by variation that new characters arise and by heredity thatthey are perpetuated. Darwin recognized two kinds of variation,both of which, being inherited and maintained through the conservingaction of natural selection, might give rise to a permanent transfor-mation of species. The first of these includes congenital or inborn 12 INTRODUCTION variations, such as appear at birth or are developed spontane-ously, without discoverable connection with the activities of theorganism itself or the direct effect of the environment upon it, thoughDarwin clearly recognized the fact that even such variations mustindire
Size: 1902px × 1314px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1902
