The paper by Colin S. Pittedrigh explores the circadian rhythms and their organizational significance in living systems. Pittedrigh emphasizes the need for bold and explicit theory formation in the study of daily rhythms, despite the vast number of observations available. He discusses the empirical generalizations about circadian rhythms, highlighting their ubiquity, endogenous nature, self-sustaining oscillations, and innate presence. The author proposes a 2-oscillator model for Drosophila eclosion rhythms, where one oscillator (A) serves as the pacemaker and the other (B) is temperature-sensitive and peripheral. This model explains the phase shifts and transients observed in response to light and temperature changes. Pittedrigh also discusses the broader implications of this model, suggesting that organisms may consist of multiple quasi-autonomous oscillatory systems, each with its own rhythm. He presents evidence from various organisms, including mammals, plants, and insects, to support the idea that circadian rhythms are fundamental to the organization of living systems. The paper concludes with discussions on the potential detrimental effects of aperiodic light conditions on the integrity of these rhythms, emphasizing the importance of mutual entrainment among oscillatory subsystems.The paper by Colin S. Pittedrigh explores the circadian rhythms and their organizational significance in living systems. Pittedrigh emphasizes the need for bold and explicit theory formation in the study of daily rhythms, despite the vast number of observations available. He discusses the empirical generalizations about circadian rhythms, highlighting their ubiquity, endogenous nature, self-sustaining oscillations, and innate presence. The author proposes a 2-oscillator model for Drosophila eclosion rhythms, where one oscillator (A) serves as the pacemaker and the other (B) is temperature-sensitive and peripheral. This model explains the phase shifts and transients observed in response to light and temperature changes. Pittedrigh also discusses the broader implications of this model, suggesting that organisms may consist of multiple quasi-autonomous oscillatory systems, each with its own rhythm. He presents evidence from various organisms, including mammals, plants, and insects, to support the idea that circadian rhythms are fundamental to the organization of living systems. The paper concludes with discussions on the potential detrimental effects of aperiodic light conditions on the integrity of these rhythms, emphasizing the importance of mutual entrainment among oscillatory subsystems.