. Text-book of embryology. Embryology. Fia. 8.—The larva and adult female of PoHunioii maenadis. (After Giard.) A, larva' jnst hatched. B, adult female, abd, ab- domen ; a(i, antennule; at\ antenna; br, brood-sac composed ot conjoined ovigerous plates of thorax; rj, jaws or gnatliites ; h, head ; pi, swimmerets or pleopods. of life by an adult could directly affect its germ cells. Lamarck's idea that the change in the body induced by new habits could effect a corresponding change in the germ cells is rejected by them. How, then, is the adaptation effected ? If an animal assumes a new habit or
. Text-book of embryology. Embryology. Fia. 8.—The larva and adult female of PoHunioii maenadis. (After Giard.) A, larva' jnst hatched. B, adult female, abd, ab- domen ; a(i, antennule; at\ antenna; br, brood-sac composed ot conjoined ovigerous plates of thorax; rj, jaws or gnatliites ; h, head ; pi, swimmerets or pleopods. of life by an adult could directly affect its germ cells. Lamarck's idea that the change in the body induced by new habits could effect a corresponding change in the germ cells is rejected by them. How, then, is the adaptation effected ? If an animal assumes a new habit or mode of hfe with success, this can only be because a new and abundant food supply is thereby opened up to it. Now Darwin has suggested that a rich food supply is the proximate cause of the arrival of variations. Hence we may provisionally assume that the new food supply upsets the stabihty of heredity by altering the chemical constitution of the hereditary substance in the germ cells, and so variations in all directions are. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
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Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
