THE RHYTHMIC UNIVERSE 371 



radiation) even from outer space, may possibly have a deter- 

 mining role in the rhythms of terrestrial organisms. The 

 mechanism, or mode according to which these various rhythms 

 function has been studied by a number of biologists and bio- 

 chemists. Their results indicate that such rhythms as color 

 change are due to the action of hormones on the chromatophores 

 (pigment organs) in the skins of the crabs and other animals 

 studied.** There is evidence in some cases to show that the hor- 

 mones themselves are produced consequent to stimuli deriving 

 from the central nervous system which has first been stimulated 

 by light from without.' When the pigment, under the action 

 of the hormones, is dispersed in the chromotophores, the skin 

 has a dark color, depending on the color of the pigment; when 

 it is undispersed and concentrated, the skin is paler. In addi- 

 tion, a kind of mid-w^ay system, the neuroendocrine system, 

 has been found to function in many activities which are 

 rhythmic.^ 



The tendency to look for the basic answers as emanating 

 from physico-chemical forces internal to the organism leads 

 the biochemist and the dissecting endocrinologist closer and 

 closer to the test tube and, it would seem, further and further 

 from the actual organism as an entity. In keeping with this 

 investigative approach, the persistent rhythms detected in 

 organisms were first thought of as produced by purely internal 

 processes, by " endogenous clocks." The organisms were pos- 

 tulated as possessing inherited mechanisms for the rhythmic 

 behavior observed, these " clocks " being considered as running 

 on their own frequencies, unaffected by outside environment. 



* Muriel I. Sandeen, " Chromatophorotropins in the Central Nervous System of 

 Uca pugilator, with Special Reference to their Origin and Action," Physiol. ZooL, 

 XXIII (1950) , 337-352. 



'' Frank A. Brown, Jr., H. Marguerite Webb and Muriel I. Sandeen, " Differential 

 Production of Two Retinal Pigment Hormones in Palaemonetes by Light Flashes," 

 Jour. Cell and Comp. Physiol., XLI (1953) , 123-144. 



® Francis G. W. Knowles, " The Control of Pigmentary Effectors," in Comparative 

 Endocrinology (New York: Wiley & Sons, 1959) , ed. by Aubrey Garbman, pp. 223- 

 232; Berta Scherrer, " The Role of Neurosecretion in Neuroendocrine Integration," 

 ibid., pp. 134-140. 



