JOHANSEN 



demonstrated the presence of well-developed mechanisms for 

 compensatory heat production. However, this heat production and 

 conservation are not governed by the same thermostatic arrange- 

 ments that are present in rabbits. 



Grant me also a few words about insulation in the naked arma- 

 dillo. The very large temperature gradients in the extremities and 

 snout shortly after the beginningof cold exposure are likely of great 

 significance (Figs. 15, 16, and 17). It is interesting to compare this 

 observation with those of Scholander and Krog on the sloths from 

 1957. These investigators suggest that the vascular bundles rete 

 mirabile in the limbs of the sloths strongly facilitate the conserva- 

 tion of central body heat at the expense of a profound cooling of the 

 limbs. The principle involved is thought to be a counter-current 

 heat exchange in the vascular bundles which provide a greatly 

 enlarged contact surface between the counter-streaming arteries 

 and veins (Scholander and Schevill, 1955; Scholander, 1958). In 

 the sloth, subcutaneous temperature gradients in the legs were as 



Figure 15. Cutaneous temperatures at various sites on the armadillo's body 

 at air temperatures of 25 C - 30 C (upper numbers) and 5° C (lower numbers). 

 (Johansen, 1961). 



116 



