RESPONSES OF HOMOIOTHERMS TO VARIATIONS 31 



the poikilo therms and the homoiotherms. Martin (1903) 

 has discovered that certain of the primitive mammals of 

 Australia have an imperfect means of heat regulation. 

 He found the duckbill to be almost cold-blooded, and the 

 Australian anteater showed a fluctuation of about 10 

 deg. C. in body temperature with a change of 30 deg. C. 

 in the surroundings. The kangaroo and other marsupials 

 exhibit a somewhat better control. The placental ani- 



BODY TEMPERATURE DEG. C. 



10 20 30 40 



-40 -30 -20 -10 10 20 30 40 50 60 



ENVIRONMENTAL ^TEMPERATURE 



Fig. 3. — Difference between body temperature and environmental tem- 

 perature in poikilotherms ( ) and homoiotherms ( ). 



mals have the most highly perfected regulatory mechan- 

 ism. The sloth {Bradypus cuculliger cuculliger Wagler), 

 one of very primitive placental forms, shows a rather 

 imperfect mechanism of heat regulation. Kredel (1928) 

 has shown that variation in the air temperature sur- 

 rounding this animal will produce a relatively marked 

 change in the body temperature. 



Homoiothermal animals respond to environmental 

 temperature variations by: (1) physiological regulation 

 of gain or loss of body heat, (2) morphological adapta- 



