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acclimation activity agamic reproduction annelids appear Arch become Biol body buds cell division cence characteristic chemical reactions colloid colloid substratum complete conjugation course curve cyanide cytoplasm death decrease definite degree of rejuvenescence determined disintegration dynamic early stages embryonic Entwickelungsmech essentially evident exist experimental experiments external conditions fact fertilization fission flatworms formation gametes gametophyte germ cells germ plasm give rise gradient higher animals hydranth increase in rate indicate individual investigation Jour labile length lower animals meganucleus metabolic rate metaplasmic method millimeters molecules morphogenesis morphological narcotics nervous system nutritive occurs organism Paramecium parthenogenesis parthenogenic period pharynx Physiol physiological condition pieces Planaria dorotocephala plants posterior end potassium cyanide problem produced proteid protoplasm protozoa rate of metabolism reduction regards relation result senescence and rejuvenescence sexually mature species spermatozoa sporophyte stages of development starvation structure substances substratum temperature theory tion tissues Uber various vegetative vegetative reproduction worms young zooid Zool
Page 41 - We have tried to show that they are not instruments, but indications — that they are no more the producers of the vital phenomena, than the shells scattered in orderly lines along the sea-beach are the instruments by which the gravitative force of the moon acts upon the ocean. Like these, the cells mark only where the vital tides have been, and how they have acted.
Page 235 - VI. The nature of the axial gradients in Planaria and their relation to antero-posterior dominance, polarity, and symmetry.
Page 4 - The most important result of the investigation is the demonstration of the occurrence of rejuvenescence quite independently of sexual reproduction. The book differs from most previous studies of senescence in that it attempts to show that in the organic world in general rejuvenescence is just as fundamental and important a process as senescence.
Page 19 - we must abandon the assumption of a living substance in the sense of a definite chemical compound. Life is a complex of dynamic processes occurring in a certain field or substratum. Protoplasm, instead of being a peculiar living substance with a peculiar complex morphological structure necessary for life, is on the one hand a colloidal product of the chemical reactions, and on the other hand a substratum in which the reactions occur and which influences their course and character both physically...
Page 12 - Loc. cit. multitudes of invisible hypothetical organisms, and therefore contribute nothing in the way of real advance. No valid evidence for the existence of these units exists, but if their existence were to be demonstrated we might well despair of gaining any actual knowledge of life. We have in this passage a clear statement of the essentiality of growth, as self-reduplication of specific substance, in the life-process.
Page 360 - The origin and early history of the germ cells in some Chrysomelid beetles.
Page 465 - ... still further. He does not even separate senescence from immaturity. Some of the most penetrating studies of growth and development have emphasized the fact that senescence and rejuvenescence are relative terms and that both processes may go on at the same time in one individual. As Child puts it, " The age changes in the organism are merely one aspect of Werden und Vergehen. The coming and passing away which make up the history of the universe.
Page 154 - P. 1893. A Contribution to the Morphology and Biology of the Stentors.
Page 189 - In the pancreas of the toad, for example, the cells, when ready to secrete, are loaded with granules, and in this condition are only very slightly active metabolically. As the cell secretion is discharged, the granules gradually disappear to a point when they are practically absent. In this condition...