VERTEBRATE PHOTOSTIMULATION 



WILLIAM S. BLLLOUGH 

 Birkbeck College, University of London, London, England 



Within the space limitations it is not possible to give more than a brief 

 introduction to what, during the past 30 years, has expanded into a 

 vast field of research. As is well known, the original experiments were 

 those of Rowan, who in 1925 reported the stimulation of the gonads 

 of the Canadian junco to unseasonable sexual maturity by means of 

 extra light in autumn. In the context of thought of those days, the 

 design of Rowan's experiments showed great originality, and in 1957, 

 the year of his death, it is particularly appropriate to pay him tribute 

 for the fundamental part he has played in the subject of vertebrate 

 photostimulation. 



Today the study of the control of vertebrate breeding cycles by en- 

 vironmental variations has become fused with studies on the physiology 

 of the ductless glands, of nutrition, of hair or feather moult, of the 

 nervous system, of behavior, and of migration. Much of this field has 

 been reviewed by Bullough (1951), and in this present additional re- 

 view only those topics which appear to be of particular relevance to 

 this conference are discussed. 



LIGHT AND VERTEBRATE REPRODUCTION 



First and foremost it is necessary to discuss the effects of light on 

 vertebrate reproduction. In Rowan's original experiments the stimulus 

 to gonad maturation was obtained by extra electric light given in the 

 evenings at a time when the natural day length was shortening, al- 

 though it should be noted that Rowan himself believed that the stimu- 

 lus was due not to increasing periods of light but to increasing periods 

 of muscular exercise (Rowan, 1928, 1929). Then arose a sharp dif- 

 ference of opinion between those who felt that the results must be held 

 to imply that it is the increasing day length of late winter and early 



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