JOHANSEN 



in making a first attempt to characterize temperature regulation in 

 monotremes. These animals, the most primitive among mammals 

 available to us for experimentation, are definitely homeothermic; 

 that is, they can regulate against environmental changes at a level 

 higher than that of the air . This is achieved by variance in heat prod- 

 uction and behavior. At air temperatures around and above the body 

 temperature such regulation fails, and homeostasis is maintained by 

 behavior. This primitive condition requires a central nervous inte- 

 grating control of both behavior and heat production. Understandably 

 these animals are confined to tropical stability and seek refuge in the 

 stability of the substratum at the high air temperatures. The other 

 member of the living monotremes, Omithoryhchus (platypus) , shows 

 some advance in regulating ability over Echidna by having sweat 

 glands . 



The marsupials show a distinct advance in homeothermism, be- 

 ing able to vary both heat production and heat loss. I will briefly 

 refer to some of the work done on temperature regulation in mar- 

 supials. 



Sutherland (1897) observed body temperatures on sixteen dif- 

 ferent species of marsupials. The average body temperature for all 

 the species was 36 G. Sutherland lists the wombat ( Phascolomys 

 plathyrinus) as the poorest regulator with an average temperature 

 of 34 C. Next came the members of the genus Petaurus or the fly- 

 ing squirrels, with an average of 35. 7 C, The koala bears (Phasco- 



larctos cinereus) had a range of from 35.0^ C to 36.5° C at air tem- 



o o 



peratures between 7.7 C and 24.5 C. Sutherland adds that upon 



exposure to the sun the body temperature rose rapidly, in one speci- 

 men to 38.4 C. Very interestingly, females always showed higher 

 temperatures than males under the same conditions, and the diver- 

 gence was always greatest when the females were suckling their 

 young. The average excess temperature from 25 observations was 

 1.2 C. The fact that pregnant or suckling females have higher tem- 

 peratures and also a more efficient regulation has often been report- 

 ed, for example, Morrison (1945) for a pregnant sloth. In the larger 

 marsupials, notably the kangaroo ( Mac r opus giganteus ) tempera- 

 tures between 36 G and 37 G were recorded. Some marsupials. 



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