MOREISON 



Figure 20 compares the form of the daily cycle in several of 

 these new world monkeys. Although at a lower level, the form of 

 the curve in Ateles is strikingly similar to that of Gebus . By con- 

 trast, curves of the two marmosets, representing the more primi- 

 tive Callithricidae, are quite distinct. Also shown in Figure 20 is 

 the night monkey ( Actus) whose cycle, however, has been shifted 

 by 12 hours so that it could be compared to the others. Nocturnal 

 forms are rare among the primates and the limited amplitude of 

 this nocturnal cycle suggests that thedaily cycle may not be merely 

 a casual concomitant of the time of activity, but be more formally 

 impressed into the "matrix" of the animal. Thus, in this instance, 

 the nocturnal Actus has reversed the characteristic primate diurnal 

 cycle, but has achieved only a limited amplitude. 



Figure 21 compares another aspect of regulation in two of 

 these species to show that while Actus has excellent "cold" regula- 

 tion, Gallithrix is quite sensitive to cold. A correlation might be 

 made with the nocturnal habit, but it is only fair to note that Actus 

 ranges up the Andean slopes to fairly cool situations. The response 

 of the smallest primate ( Cebuella ) to cold is shown in Figure 22 

 and shows even less resistance to cold than the larger Gallithrix. 

 But its resistance to heat stress is distinctly superior, and at a 



T , of 40 G it maintains a T of 40° G. 

 A B 



Figure 23 shows the - metabolic response of Gebuella at vary- 

 ing T and presents a good example of the problem of fitting a 

 conductance value to a thermolabile animal. If we describe our 

 homeotherm in terms of the simplest model then the heat flow or 

 metabolism will be proportional to the temperature differential 



(Scholander et al., 1950a). But, as was seen in Figure 22, the main- 



o o 



tenance range for T in Gebuella was only between 15 G and 30 G, 



and below this we will find reduced T and metabolism. Accordingly, 



if the metabolism is plotted directly against T the mean curve will 



have too low a slope (low conductance) and will extrapolate above 



the T . To adjust for this error, the metabolism may be plotted 



against the temperature differential, T -T (top scale in Fig. 23); 



or to maintain a more familiar scale, the T may be corrected by 



the amount of the T depression (bottom scale in Fig. 22). With 



)od 



this procedure, a good linear representation is obtained with extra- 

 polation to the T (38 G) at the abscissa. The conductance curves 

 B 



408 



