JOHANSEN 



at that time. Semon expressed the hope that the monotremes would 

 be just as important for the study of homeothermism in mammals 

 as they had been to the study of comparative anatomy and develop- 

 mental history. If Semon lived today, he would have been very much 

 disappointed. In spite of a few very interesting studies that followed 

 shortly after him, practically nothing has, to my knowledge, been 

 done in the last 30 or 40 years , when the general study of tempera- 

 ture regulation has flourished so greatly. Sutherland (1897) rep- 

 orted 29.4 G to be the average temperature of 14 specimens of 

 Echidna. One cold morning an animal could be as low as 22 C; 



whereas another one exposed to the mid-day heat registered as 



o 

 high as 36.6 G. This was to Sutherland an immense range for a 



mammal and suggested a reptilian lack of ability to regulate against 

 temperature changes. Let me add that Sutherland did what practi- 

 cally all of us do who study temperature regulation. He completely 

 curtailed the animal's ability to regulate its body temperature by 

 natural behavior. I hope to demonstrate repeatedly the importance 

 of this factor. 



Maybe we should digress to put the importance of natural behav- 

 ior in a proper relation to a phylogenetic discussion of temperature 

 regulation. Let us then restate some of the essentials in the out- 

 standing works of Gowles and Bogert (1944) on temperature regula- 

 tion in terrestrial reptiles. The essence of their work is that terres- 

 trial reptiles, that is, lizards and snakes, can and do keep remark- 

 ably constant body temperatures during activity. Bogert (1949) 

 introduces some clarifying terms when he refers to the birds and 

 mammals as largely endothermic as opposed to the reptiles, which 

 derive their body heat mostly from external sources and can thus 

 be termed "ectothermic." The author points in particular to the 

 importance of the solar radiation, which may raise a reptile's tem- 

 perature to levels manydegrees higher than that of the air. It seems 

 reasonable to accept the suggestion from Bogert that the acquisi- 

 tion and perfection of the complicated machineryfor a high internal 

 metabolic heat production has its antecedent in the ectothermic 

 assessment of heat present today in the reptiles. The behavioral 

 control of body temperature in reptiles implies a high degree of 

 sensitivity to temperature changes. Sutherland's data seem to jus- 

 tify the conclusion that the monotremes display variable body tem- 

 peratures in response to a great range of air temperatures. In 1901 



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