652 



PHOTOPERIODISM IN VERTEBRATES 



N 



D 



' F ' 



M 



AMNUAL CYCLE OF DAYLEriGTHS 

 AT 42° liORTH LATITUDE 



5CALE OF PH0T0PERI0D5 

 AT HOUR INTERVALS 



NOTROP/5 BIFREtiATUS 

 IN NATURE 

 HARRIMGTOM, 19-^7 



b' 



APR. 22 



S' 



m- 



JUNE 



7-30 



MAY 22 JULY 13 



c 



AUG.5 



/y. BIFREfiATUS 

 EXPERIMENT 

 HARRinGTON,l9S0 



L 



5' 



JAN.22 

 JAM. I FEB.14 



yVW =E'25' 



sacrificed 



5EPT.2G 



MOV. 24 

 NOV. 17 JAN 



sacrificed 

 Jan. 4 



rf. BIFREnATU5 



EXPERIMENT 



HARRINGTON, 1957 



OCT. 4 



^ 



5' 



sacrificed 

 Dec. 1 4 



MOV. 17 



NOV 10 



EtiNEACAnrHUS OBESUS 

 EXPERIMENT 

 HARRIMSTON, 1956 



REFRACTORY PERIOD — ^ PRE5PAWNING PERIOD s]^ SPAWMING PERIOD 



Fig. 1. Chronologies of natural and experimentally induced breeding 

 periods of the brfdled shiner, Notropis bifrenatus, and of an experi- 

 mentally induced breeding period of the banded sunfish, Enneacanthus 

 obesus. Dates of imposition of supraliminal photoperiod, L.; of earliest 

 and latest recorded nuptial coloration, c and c', sexual behavior, b and 

 h\ and spawning, S and S'. (After Harrington, 1957.) 



