Reptile Activity 
187 
ing the mammillary bodies extended the 
period of voluntary hypothermia in the 
desert iguana, Dipsosaurus dorsalis (Kluger, 
Tarr, and Heath, 1973). 
Temperature-activity relationships 
Several types of reptiles may be active at 
night but bask at least occasionally during 
the day. The implications are interesting. 
We usually assume that central nervous sys- 
tem (CNS) activity in reptiles or mammals 
is limited at low temperatures, but in these 
nocturnal reptiles the greatest activity may 
be at low temperatures, suggesting a circa- 
dian rhythm of arousal inversely related to 
high body temperature. 
Crocodiles, during some months of the 
year, bask on land for much of the day but 
are active primarily at night in the water 
(Regal, 1968 ; Lang, 1976), while a snake such 
as the sidewinder Crotalus cerastes regulates 
its body temperature by basking (Cowles 
and Bogert, 1944), but is largely active at 
night. I observed that an individual boa con- 
strictor in a thermal gradient basked and 
elevated its body temperature only after feed- 
ing. It had not previously basked even in 
preparation for activity (Regal, 1966). 
In contrast, we know comparatively little 
about the natural history of nocturnal lizards 
and other reptiles. Various nocturnal geckos 
(Brattstrom, 1952; Bustard, 1967) as well as 
the tuatara may have activity rhythms in- 
versely related to basking behavior. Also, 
some diurnal turtles and the marine iguana, 
among others, may forage in cool water, yet 
bask at higher body temperatures. 
Influence of the third eye on activity 
and thermoregulation 
Many species of lizards possess a third eye 
that appears as a small differentially pig- 
mented speck on the top of the head. The 
eye is part of the pineal system, and there 
is an extensive literature on the pineal sys- 
tem of vertebrates. A number of studies have 
shown that the parietal eye is biochemically 
highly active and electrophysiologically re- 
sponsive. (See reviews by Wurtman et al., 
1968; Eakin, 1973; Gundy, 1974; and Justis 
and Taylor, 1976.) 
Most studies suggest that the third eye is 
involved in a negative feedback system regu- 
lating activity-temperature energetics. An 
interesting question is how the behavior of 
lizards such as the macroteiids, which lack 
the eye, may differ from typical lizards. 
Stebbins and Eakin (1958) were the first 
to show behavioral effects of removal of the 
eye. These authors reported that in the 
iguanid lizards, Sceloporiis occidentalis, S. 
virgatus, Uta stanshuriana, and Uma inor- 
nata, removal of the eye resulted in an in- 
creased exposure to sunlight in the field or 
artificial light in the laboratory. In the pari- 
etalectomized lizards, the length of time spent 
in the normal activity body temperature 
range was extended. Compared with sham- 
operated animals there was a three-fold in- 
crease in displacement from previously deter- 
mined home ranges. There was also less 
tendency to retreat when approached by an 
observer. Similar results were obtained by 
shielding the eye with foil. Subsequently, 
the authors themselves found it difficult to 
replicate these findings (Stebbins, 1963; 
Stebbins and Wilhoft, 1966). 
In a recent study, Stebbins and Cohen 
(1973) parietalectomized and sham-operated 
Sceloporus occideritalis in the fall, released 
them, and recaptured them in the spring. 
Thyroid activity and reproductive condition 
in the females were seasonally accelerated 
in the experimental animals. As in an earlier 
study (1958), many of the experimental liz- 
ards seemed strongly attracted to bright 
sunlight and reluctant to take cover. 
Recently, Hutchinson and Kosh (1974) 
monitored body temperatures of Anolis 
carolinensis over the 24-hour cycle. In pari- 
etalectomized animals, cycles were altered 
and the selection of temperatures below the 
“minimum voluntary level” in the dark was 
eliminated. Also, the peak of body tempera- 
ture occurred somewhat later in the day. 
Preferred temperatures during activity were 
