November i8, 1897] 



NA TURE 



67 



doubly glad that he had lately succeeded in convincing the 

 Government that somewhere in Germany there must be a place 

 where every student could at all times find instruction on 

 questions of pathology and medicine, that he had been in- 

 strumental in securing the rebuilding of the pathological 

 museum. 



THE TEMPERATURES OF REPTILES, MONO- 

 TREMES AND MARSUPIALS} 



""PHERE has for many years past been a tendency to diminish 

 or ignore the distinction between the cold-blooded and the 

 warm-blooded types of animal life. Yet the difference is one 

 that is not only real, but in some respects radical. In very few, 

 however, of nature's classes is there found a line of sharp de- 

 marcation, and the chief purpose of this paper is to point out 

 that, though the distinction between the two types is real, there 

 lies between these two types a line of steady gradation. 



Although the invertebrates have the capacity of producing 

 heat, they are themselves cold-blooded. With the exception of 

 the insects, they very rarely rise more than a fraction of a degree 

 above the temperature of the media in which they happen to be. 

 According to observations of Prof. Valentin, polypi, medusae, 

 echinoderms, molluscs, crustaceans and cephalopods are able to 

 raise themselves about a fifth of a degree, sometimes as much as 

 three-fifths of a degree, above their environment. - 



Among insects the power of heat-production is very much 

 greater. Though essentially cold-blooded creatures, in the sense 

 that they have no fixed standard of body-heat towards which 

 they approximate, they are almost always warmer than their 

 media ; but if they are at rest that excess is only a degree or two. 

 In case, however, of severe exertion, they are capable of warming 

 themselves to a remarkable extent. 



In the case of fish, amphibia and reptiles the same is true. 

 At rest all of them remain at the temperature of their environ- 

 ment, rising and falling with it, and showing no capacity, 

 however rudimentary, of maintaining a fixed and characteristic 

 temperature ; yet all can warm themselves by exertion. The 

 large blue-tongued lizard, which is common in the southern parts 

 of Victoria [Cyclodus gtgas), can warm himself as much as half a 

 degree in ten minutes of anger. In five experiments of this sort 

 I found that different individuals had different capacities of being 

 irritated, but the average was a trifle under half a degree for ten 

 minutes of exasperation. 



By activity, and consequent heat-production, all fish, amphibia 

 and reptiles seem able to keep themselves a little warmer than the 

 air or water in which they dwell. Dutroche tells us {Ann. des 

 Sciences Nat., xiii. p. 20) that the newt can keep itself from 2° 

 to 5^' above the temperature of its medium, the turtle 1^° to 3^°, 

 and the common green lizard of France (Lacerta viridis) from 4° 

 to 7". Max Furbinger asserts that species of blind-worm rise as 

 much as 8° above the temperature of the air. Fish at rest 

 appear to take almost absolutely the temperature of the water 

 wherein they live, but after a struggle, or any other form of 

 energy, they may warm themselves two or three degrees. 



This, however, has no real affinity with a warm-blooded habit. 

 And yet these creatures approach in a remote way the warm- 

 blooded condition by sometimes developing a capacity for heat- 

 production in the action of their viscera. Dumeril has shown 

 that snakes by mere digestion can warm themselves from 2° to 4°, 

 the maximum temperature occurring about twenty-four hours 

 after a meal. 



Thus it constantly happens that these animals, though essen- 

 tially cold-blooded, may be observed at temperatures somewhat 

 above that of their environment. But in general that excess is 

 not great, and it leaves the distinction between the warm-blooded 

 and ihe cold-blooded type quite unaffected. 



The true criterion of the difference is of course the concomi- 

 tance of the temperature of the animal and its medium. An 

 animal of the warm-blooded type may vary a trifle in its general 

 body temperature when the climate alters, but it maintains an 

 almost constant degree of heat. The reptile, though it may 

 maintain itself a few degrees above the surrounding temperature, 

 always varies with it, rising and falling so as to keep always the 

 same number of degrees in excess. 



To see how far this concomitancy held, I placed two 



1 By Alexander Sutherland. Abridged from the Proceedings of the Royal 

 Society of Victoria, vol. i.x. (New Serie.s), 1897. 

 - All degrees in this paper are Centigrade. 



NO. 1464 VOL. 57] 



specimens of the large lizard already mentioned into a small 

 tank of water, so that only their noses were above water. I 

 then warmed up the water at various rates of speed by means of 

 one or more lamps. The accompanying diagram (Fig. i) shows 

 how closely the lizards followed the temperature of the enclosing 

 water. 



Cyclodus gi^as is a very sluggish creature, and if left alone 

 never warms himself by any exertion, yet if one takes his 

 temperature in the early part of the day it will almost always 

 be found to be below that of the air. After sunset it is 

 generally higher. During two years I kept specimens of this 

 species in a box, sometimes six or eight, sometimes only two 

 or three. I took their temperatures morning and evening, 

 not altogether continuously, but throughout the larger portion 

 of that time. The average of all these observations gave for 

 lizards i8°"i, for the air i8''"4. This is a very close approxima- 

 tion considering that the temperatures had the wide range that 

 lies between 12° and 32°. The lizards appear to be a little 

 colder than the air. This I believe to be due only to the fact 

 that, taking temperatures before eight o'clock in the morning, 

 the lizards were still considerably in the rear of the 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 



i a. •^66788 10 hours 



Fig. 1. — To show concomitance of temperatures of lizards and water. 

 Upper line, temperature of water ; lower line, temperature of 

 lizards. 



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. 



The steps whereby the more active and intelligent warm- 

 blooded types have arisen from the lethargic level would form a 

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

 easier and more prosaic one of recording that such steps, how- 

 ever 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 

 observations, 24°'8 when the water in which the animals were 

 kept averaged 22°"2(y^;/r«a/of LinneanSocietyof 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 38° 9, as calculated from Dr. John Davy's lists 

 (Edin. Phil. Journal, 1825, p. 30x3), while the average of a 

 similar but shorter list supplied by Max Furbinger is 39°. We 



