PHOTOPERIODISM IN REPTILES 673 



terrestrial invertebrates face similar photoperiodic problems, but the 

 length of most reptilian life cycles and the slowness with which they 

 reach sexual maturity probably sets them apart. 



The considerations presented above lead to the conclusion that even 

 in the few instances in which a photoperiodic response in reptiles has 

 been demonstrated in the laboratory, the interpretation of its reproduc- 

 tive importance requires that it be fitted into the pattern of daily 

 activity under natural conditions; this in turn requires knowledge of 

 the physiological and particularly the behavioral responses to tempera- 

 ture characteristic of the species being studied. 



The complications imposed on the analysis of reptilian photo- 

 periodism by behavioral temperature regulation are formidable, but 

 recent work on the function of the pineal organ of lizards complicates 

 the problem even further. It has been found (Stebbins, 1957; Stebbins 

 and Eakin, 1958) that surgical removal of the parietal eye from lizards 

 of several species (Scelopoms occidentalis, Sceloporiis imdulatus, Uta 

 stansbwiana, and Uma inomata) caused a significant extension of the 

 duration of the daily periods which they spent exposed to sunlight but 

 did not alter the range of body temperatures characteristic of normal 

 activity. Thus in these lizards, and possibly in other iguanids, the 

 effective photoperiod is determined in part by the response of the 

 parietal eye as well as by the thermoregulatory behavior discussed in 

 preceding paragraphs. In view of these findings it is of interest that 

 about twenty years ago Clausen and Poris (1937) reported that pineal 

 extirpation enhanced the photoperiodic response of male Anolis. It 

 appears that an adequate analysis of the role of day length in the 

 reproduction of lizards requires data on (1) activity temperatures, 

 (2) the extent to which behavioral thermoregulation controls daily 

 exposure to light, (3) the relations of the pineal body to activity pat- 

 terns, and (4) the secretory responses of the pituitary to light. 



In view of the restrictions placed on day length by behavioral 

 factors related to thermoregulation, it would appear that photo- 

 periodism in reptiles could best be investigated in an environment 

 that allows normal activity at all seasons without elaborate thermo- 

 regulatory behavior. Such a condition is found in the humid Tropics. 

 One of the Central American species of Anolis, Ameiva, or particu- 

 larly Scelopoms would seem to be a likely form for experimental use. 



