Temperatures of Reptiles, etc. 61 



rear of the air temperature, while between five and six o'clock in 

 the evening, though they were above the air temperature, the 

 excess then did not wholly balance the morning deficiency. 



I am convinced that if one took the temperature of a quiet 

 lizard every hour for a month, the average would correspond 

 almost exactly with the average temperature of the air. The 

 morning and evening observations which I took would give a less 

 exact result, though from them the difference is only three-tenths 

 of a degree. 



A cold-blooded animal is therefore one which when at rest takes 

 its temperature almost absolutely from its environment. When 

 a snake is asleep, the slow beat of its heart, eight or ten times in 

 a minute, will generally, so far as I have noticed, keep the muscles 

 of the heart itself about six or eight tenths of a degree warmer 

 than the rest of the body. This, diffused through the whole body, 

 must have a tendency to slightly increase its temperature, but 

 only to a minute extent. The same snake, however, after a time 

 of activity may be two or three degrees above the heat of the 

 surrounding air. Yet even that is inconsiderable compared with 

 the extreme rise and fall of the creature's temperature with the 

 alternations of day and night, of hot or cold weather. 



The steps whereby the more active and intelligent warm- 

 blooded types have arisen from this lethargic level would form a 

 fascinating subject for enquiry, but I purpose here only the much 

 easier and more prosaic one of recording that such steps, however 

 caused, do actually present themselves, and that these are in the 

 most perfect accordance with the existing classification, which is 

 based on anatomical considerations alone. 



The monotremes are, in consideration solely of their more 

 reptilian anatomy, placed lowest in the scale of mammals. Their 

 low temperature would entirely justify, were justification in any- 

 way needed, the position thus assigned them next to the reptiles. 

 The temperature of the duck-billed platypus has been determined 

 by Baron Miklouho-Maclay to be, as the average of three observa- 

 tions, 24-8° when the water in which the animals were kept 

 averaged 22-2°. (Journ. of Linnrean Soc. of N.S.W., VIII., p. 

 425, and IX., 1204.) 



Now, the average of forty-five specimens of the ten higher orders 

 of the mammalia, excluding the monotremes and marsupials, is 



